# Main > General Discussion >  Program to calculate size of map and point to point distance.

## Elros

Hello, i have a little problem, sorry for my english is not my first lenguage, im italian. 
Anyone know one program can calculate travel time, or distance point to point of my map?

I have made my own map hand drawn and updated with Photoshop.
Now i want determinate the size of my map basing on 1 day of travel is 15-20 Kilometers, approximately 10-12 miles.

Is that possible with one cartography program?

Edit: 
I am also open to external programs besides photoshop

----------


## Azélor

Measuring area is somewhat easy. 

1-The first requirement is knowing what map projection you are using.
I am going to assume you are using an equirectagular map projection. There are no default map projection but this is a very common one to use unless you have something specific in mind.

2- You need to change the projection of an image using a software like G.Projector : https://www.giss.nasa.gov/tools/gprojector/
G.projector now accepts plenty of different projections as input not just equirectangular. 
Pick an equal area map projection such as Mollweide https://en.wikipedia.org/wiki/Map_projection#Equal-area
It will allow you to measure areas. 
ALWAYS KEEP THE ORIGINAL, WORK ON A COPY

3- open the image in photoshop.
On a new layer, paint the area you want to measure in a different colour. Use the pen, not the pencil as you need sharp (pixelated) borders if you want to be accurate.
Using the magic wand and the histogram (windows/histogram) find the total surface (in pixel) of the map (water and earth). Write it down somewhere.
Find the size of the area you are interested in. 

Divide the area by the size of the world, this gives you a percentage. 
Multiply this percentage by the size of the world in square kilometre, ( or square miles in you live in US or Myanmar) to get the actual size of the area.
For reference, Earth is 510 000 000 km2. So 10% would be 51 000 000 km2.

You don't really need to know the scale of your map, just the % of the world covered and the size of the world.

The find a distance between two points: I think it can be done by using trigonometry where ''a'' is the difference in latitudes, ''b'' is the difference in longitudes and ''c'' is the distance that you are trying to find. 
The ''b'' will change depending on the latitude as the distances get shorter the closer you get to the poles.

----------


## Elros

> Measuring area is somewhat easy. 
> 
> 1-The first requirement is knowing what map projection you are using.
> I am going to assume you are using an equirectagular map projection. There are no default map projection but this is a very common one to use unless you have something specific in mind.
> 
> 2- You need to change the projection of an image using a software like G.Projector : https://www.giss.nasa.gov/tools/gprojector/
> G.projector now accepts plenty of different projections as input not just equirectangular. 
> Pick an equal area map projection such as Mollweide https://en.wikipedia.org/wiki/Map_projection#Equal-area
> It will allow you to measure areas. 
> ...




Hi, thanks for replying, I'm using this map here.




I don't know what projection it is, I don't understand much about these things.  :Frown: 
Isn't there an easier method?

----------


## Azélor

I don't think there is a faster method. Photoshop was not designed for cartographers but for artists in general, therefore it lack some tools and we have to use others software. 
While this method looks complicated, it gets really easy once you do it a couple of times.

----------


## Falconius

You should note that Azelor is talking about a whole world map.  So if you were to go with that method to get the area of the island, you'd have to put the island by itself in a world map.

----------


## Azélor

> You should note that Azelor is talking about a whole world map.  So if you were to go with that method to get the area of the island, you'd have to put the island by itself in a world map.


Oh, you are right. It's going to be a little bit more complex. 
You don't need to have the whole world, you can do it using only a portion of it. 
G.projector will ask to enter the edges of the map (longitudes and latitudes).
If you can figure out the coordinates, you can do it with only a section of the map.
But you will also have to find the percentage of the world covered by that specific section.

----------


## waldronate

Your island is less than about 400 miles across: the errors inherent in the map image will overwhelm any likely measurement errors relating to projection. In short, because the island is smallish, you can mostly ignore the projection. If the world itself is flat, then projection is an irrelevant concept.

Now that your map is declared as something that can be measured with a ruler, you need a tool that will measure those distances. There are many tools out there that will do that (try searching for "measure distance on an image web page" in your favorite search engine. Then define that one pixel in your image is X real-world units as shown by your scale bar.

A less complex technique use a physical ruler to measure the scale bar and your desired path directly onscreen, then do the math to convert scale units to real-world units. This also works if you print out the map. The scale bar is the critical part here.

----------


## Redrobes

Also if you want to measure area then get your map into a black and white image where the island is all black and the background is all white - using contrast or just painting it in. Then you can use the histogram view on most paint packages to count up the percent of the image which is white and black. From that you can usually calculate the area of a complex shaped island real quick.

So if you have a 1000x1000 image and you have a scale bar showing that 100 pixels across is 10 miles then each pixel is 10 / 100 miles or 0.1 miles each pixel. So if your histogram reads off that your island in black is 27.3% of the total white background image, then you have 27.3% of 1000 x 1000 x 0.1 x 0.1 square miles. Which is 0.273 x 100 x 100 which is 2730 square miles.

----------


## Elros

> I don't think there is a faster method. Photoshop was not designed for cartographers but for artists in general, therefore it lack some tools and we have to use others software.


Are there other softwere that can help me?




> While this method looks complicated, it gets really easy once you do it a couple of times.


I think trying nothing costs to me. Thanks for the advice  :Very Happy:

----------


## Elros

> Oh, you are right. It's going to be a little bit more complex. 
> You don't need to have the whole world, you can do it using only a portion of it. 
> G.projector will ask to enter the edges of the map (longitudes and latitudes).
> If you can figure out the coordinates, you can do it with only a section of the map.
> But you will also have to find the percentage of the world covered by that specific section.


It seems complex

----------


## Elros

> Your island is less than about 400 miles across: the errors inherent in the map image will overwhelm any likely measurement errors relating to projection. In short, because the island is smallish, you can mostly ignore the projection. If the world itself is flat, then projection is an irrelevant concept.
> 
> Now that your map is declared as something that can be measured with a ruler, you need a tool that will measure those distances. There are many tools out there that will do that (try searching for "measure distance on an image web page" in your favorite search engine. Then define that one pixel in your image is X real-world units as shown by your scale bar.


So the dimension are important? 
I make this island tiny, but for my book i thinking somethin like europe dimension, if i make that maps the dimension of measure is a problem?





> A less complex technique use a physical ruler to measure the scale bar and your desired path directly onscreen, then do the math to convert scale units to real-world units. This also works if you print out the map. The scale bar is the critical part here.


Yea is more simply this method, but i have to decide the scale bar of the map before, right?

----------


## Elros

> Also if you want to measure area then get your map into a black and white image where the island is all black and the background is all white - using contrast or just painting it in. Then you can use the histogram view on most paint packages to count up the percent of the image which is white and black. From that you can usually calculate the area of a complex shaped island real quick.
> 
> So if you have a 1000x1000 image and you have a scale bar showing that 100 pixels across is 10 miles then each pixel is 10 / 100 miles or 0.1 miles each pixel. So if your histogram reads off that your island in black is 27.3% of the total white background image, then you have 27.3% of 1000 x 1000 x 0.1 x 0.1 square miles. Which is 0.273 x 100 x 100 which is 2730 square miles.


Math, my enemy  :Razz:  , Thanks it will take a few days before i understand but i think is verry helpfull.
So this method is used to calculate the area of island?
If i need to calculate in straight line? something like the length of a river?

----------


## Elros

I have to ask at all of you, exist any external program? 

I know about Campaign Cartographer and Fractal terrain i found on forum list of program on this forum, that program can help me to measure maybe?

I thinking about to use that two program to make my next map.

----------


## waldronate

Fractal Terrains has a ruler tool that will measure distances on a world (globe or plane). CC3 will measure planar distances and areas.
I like to recommend that people buy a copy of Fractal Terrains when possible, but I did write the program and I do receive income from its sales, so my recommendation may be a bit suspect.

----------


## Elros

> Fractal Terrains has a ruler tool that will measure distances on a world (globe or plane). CC3 will measure planar distances and areas.
> I like to recommend that people buy a copy of Fractal Terrains when possible, but I did write the program and I do receive income from its sales, so my recommendation may be a bit suspect.


:O good, can i import my map in that program?
I mean CC3 and Fractal Terrain.

----------


## waldronate

Both programs will import images, yes. Fractal Terrains can be a bit more complex due to it's projection requirements, but it's not too hard. I can walk you through how to do it if needed (and then everyone will have a reference).

----------


## Elros

> Both programs will import images, yes. Fractal Terrains can be a bit more complex due to it's projection requirements, but it's not too hard. I can walk you through how to do it if needed (and then everyone will have a reference).


 :Surprised:  Wanderful  :Surprised:  
Momentarily i can't afford to buy them but i really do care.

I have to chose the scale of map? 

As I understand it i can chose the scale, and measure my map right?
And if i import a map from Fractal Terrain to CC3 the scale of map are marked?
Can i import a map from Fractal Terrain to Photoshop with the scale pregenerated in Fractal Terrain?

Sorry for my many question  :Very Happy:

----------


## waldronate

You can probably still download the Fractal Terrains demo from the profantasy website. The exports are limited in size and are disabled after the trial period, but the onscreenstuff still works
 The demo is for an older revision, I think, but may well be useful.

----------


## Elros

> You can probably still download the Fractal Terrains demo from the profantasy website. The exports are limited in size and are disabled after the trial period, but the onscreenstuff still works
>  The demo is for an older revision, I think, but may well be useful.


 :Surprised:  One demo, i like it, but i have to be Prepared for that i have only 1 month to do all, right?

Sorry if i repost my old question down here, can you tell me something about?  :Very Happy: 

As I understand it i can chose the scale, and measure my map right?
And if i import a map from Fractal Terrain to CC3 the scale of map are marked?
Can i import a map from Fractal Terrain to Photoshop with the scale pregenerated in Fractal Terrain?

----------


## waldronate

You can keep using the demo after the month trial, you just can't export or save data. You can keep measuring distances and viewing things as long as you like. Nothing ever prevents you from taking a screenshot of the program to collect data.

To import your data, you need to do a little math. Your scale bar says that it's 120km across. Loading the map in Photoshop, selecting the scale, copying it, and making a new map from the copy shows that your scale bar is 197 pixels across (for simplicity of the math, I'll declare it to be 200 pixels wide). That means that each pixel in your map is just about 0.6km across (120km/200pix=0.6km/pix). Your whole map is 2000pix by1500 pix, meaning that the map is 1200km by 900km.

For a spherical Earth-sized world (40000 km around at the equator and from one pole through the other and back again), that means that your map is 1200/40000*360=10.8 degrees across and 900/40000*360=8.1 degrees high. Why do you care about that? Because FT's image import assumes that the map edges are specified in degrees. Because we've declared that the map is "flat enough", we don't have to worry about the consideration that FT wants Equirectangular projection images as its input. Because we're only concerned about  measuring distances, we can center the image at the equator to reduce errors. If you want to put that image at a specific point in the world, you'll need to reproject that base image using a program such as ReprojectImage ( http://fracterra.com/ReprojectImage.zip ).

Due to a quirk in FT's image process, you need to flip the top and bottom edges to get things upright.

The image below shows how you'd attach your map to an FT world on the left and a measurement across the central lake using FT's ruler tool.

You have a map that already has a scale on it. As described above, your scale can be used to make the map the correct size for a world. If you export from FT to CC3, the scale should be correct for that map. The FT demo is very resolution-limited, so outputting to CC3 from the demo isn't a whole lot of use. You already have a map in Photoshop with the scale on it (that's how you made the JPEG, right)? When the map is imported into F, the original calculations above were done to ensure that FT's understanding of your map was a close match to the information originally expressed in your scale bar.

----------


## MistyBeee

I have absolutely no idea if I can help in your specific case (because my husband is speaking _loudly_ with a student at the moment and I'm unable to focus enough and read the full thread ^^'), but Photoshop itself has a tool for measures of distances & areas. Have a look there maybe :
- In Italian,
- In English,
- In French.

----------


## Elros

> You can keep using the demo after the month trial, you just can't export or save data. You can keep measuring distances and viewing things as long as you like. Nothing ever prevents you from taking a screenshot of the program to collect data.
> 
> To import your data, you need to do a little math. Your scale bar says that it's 120km across. Loading the map in Photoshop, selecting the scale, copying it, and making a new map from the copy shows that your scale bar is 197 pixels across (for simplicity of the math, I'll declare it to be 200 pixels wide). That means that each pixel in your map is just about 0.6km across (120km/200pix=0.6km/pix). Your whole map is 2000pix by1500 pix, meaning that the map is 1200km by 900km.
> 
> For a spherical Earth-sized world (40000 km around at the equator and from one pole through the other and back again), that means that your map is 1200/40000*360=10.8 degrees across and 900/40000*360=8.1 degrees high. Why do you care about that? Because FT's image import assumes that the map edges are specified in degrees. Because we've declared that the map is "flat enough", we don't have to worry about the consideration that FT wants Equirectangular projection images as its input. Because we're only concerned about  measuring distances, we can center the image at the equator to reduce errors. If you want to put that image at a specific point in the world, you'll need to reproject that base image using a program such as ReprojectImage ( http://fracterra.com/ReprojectImage.zip ).
> 
> Due to a quirk in FT's image process, you need to flip the top and bottom edges to get things upright.
> 
> The image below shows how you'd attach your map to an FT world on the left and a measurement across the central lake using FT's ruler tool.
> ...


I didn't realize how small my test map was before seeing it on the Fractal Terrain globe  :Surprised:  .

Wanderful, so FT is everything i need  :Surprised:  .
Thanks verry verry thenks  :Very Happy:  I will try to buy it in the future.

One last question  :Very Happy:  , from how i have undstand more small are the map more precise are the measuration, right?
That becouse in the future i wanna make one map more large then this _(the map for my book, becouse this map is only a test map, for testyng my abilitys and learn how to make a map)_, maybe the size of south america more or less, do you advice me to create that map in FT and export in photoshop? Bypassing CC3? Can i?

If i export my map in Photoshop from FT, i dont loose the scale? Maybe if i wanna reupload the map in FT to measure? 
That becouse my plan is to create my own world in FT and use only one continent for my book and preserve me the rest of the world to the future.

For that reason im searching a method to measure the map, is verry important to me  :Very Happy:  .


Thenks again for all  :Very Happy:   :Very Happy:  .

----------


## Elros

> I have absolutely no idea if I can help in your specific case (because my husband is speaking _loudly_ with a student at the moment and I'm unable to focus enough and read the full thread ^^'), but Photoshop itself has a tool for measures of distances & areas. Have a look there maybe :
> - In Italian,
> - In English,
> - In French.


 :Surprised:  interesting  :Surprised:  
Thenks i did not know. I will try.

Edit: i have the standard edition i cant use that function  :Frown:

----------


## waldronate

One of the problems of a map on a globe is that traditional fantasy map decorations like a scale bar and compass rose start to lose meaning as a map covers a larger and larger area of the globe. This change in meaning has to do with the map projection (the transformation from a sphere to a flat map). The scale bar and compass rose are useful for maps that over a small area because the direction is well-defined and the scale doesn't change enough to matter. https://www.reddit.com/r/MapPorn/com...ing_continent/ shows a worst-case example of what can happen to a compass rose (a compass rose on this map wouldn't be useful because there isn't a single direction "north"). Cylindrical map projections such as the well-known Mercator and Equirectangular projections are examples where a scale bar isn't very useful because the scale on such a map is true only at one latitude and is progressively more wrong as you approach the poles.

I don't know that CC3 would be useful for your problem unless you want to use it to create or decorate maps. If you're already comfortable using Photoshop for mapmaking, CC3 might not add much. FT3 can be useful for keeping multiple maps consistent in projection. For example, a rough outline of the world in FT can be used to get template images in a desired projection and then those template images can be fleshed out in Photoshop to get your final maps.

You can then (if desired), push those final maps back into FT and measure on their surface. If you use a projection other than Equirectangular for your Photoshop map, you will need to reproject the image back to Equirectangular before importing it into FT, but that's not too difficult to do.

In any case, FT will be able to give you accurate physical distances as long as your inputs are well-defined. It's like a low-end GIS system in some ways.

One thing to consider is that a physical distance across the map likely doesn't have a direct mapping to time of travel. A horse travels very different distances along roads on a grassland as opposed to forging across high mountains or swamp. FT doesn't have a "time of travel" calculator, just a distance measurement tool.

----------


## Elros

> One of the problems of a map on a globe is that traditional fantasy map decorations like a scale bar and compass rose start to lose meaning as a map covers a larger and larger area of the globe. This change in meaning has to do with the map projection (the transformation from a sphere to a flat map). The scale bar and compass rose are useful for maps that over a small area because the direction is well-defined and the scale doesn't change enough to matter. https://www.reddit.com/r/MapPorn/com...ing_continent/ shows a worst-case example of what can happen to a compass rose (a compass rose on this map wouldn't be useful because there isn't a single direction "north"). Cylindrical map projections such as the well-known Mercator and Equirectangular projections are examples where a scale bar isn't very useful because the scale on such a map is true only at one latitude and is progressively more wrong as you approach the poles.
> 
> I don't know that CC3 would be useful for your problem unless you want to use it to create or decorate maps. If you're already comfortable using Photoshop for mapmaking, CC3 might not add much. FT3 can be useful for keeping multiple maps consistent in projection. For example, a rough outline of the world in FT can be used to get template images in a desired projection and then those template images can be fleshed out in Photoshop to get your final maps.
> 
> You can then (if desired), push those final maps back into FT and measure on their surface. If you use a projection other than Equirectangular for your Photoshop map, you will need to reproject the image back to Equirectangular before importing it into FT, but that's not too difficult to do.
> 
> In any case, FT will be able to give you accurate physical distances as long as your inputs are well-defined. It's like a low-end GIS system in some ways.
> 
> One thing to consider is that a physical distance across the map likely doesn't have a direct mapping to time of travel. A horse travels very different distances along roads on a grassland as opposed to forging across high mountains or swamp. FT doesn't have a "time of travel" calculator, just a distance measurement tool.


I could use city names instead of geographic coordinates to solve the problem of the many north direction.
How much inaccurate are the scale bar in a map like south america? 

I dont need precision, i suppose approximately 10 miles is 1 day of walk, maybe more maybe less.
The important thing is: if the reader wants to establish the distance between two places, he can do it without destroying the credibility of my story.
In north america 100 km in straight line to the north direction, in an equirectangular map, how much are in the real world? I can afford a bit of error space, since the story takes place in the Middle Ages.


Last question: if i import a map from FT to photoshop, how can i find out the scale of map? Is indicated somewhere?

In any case, thanks for all the patience you're having with me. I'm really grateful.  :Smile:

----------


## waldronate

http://desktop.arcgis.com/en/arcmap/...F-FC70BE1F7E8D offers suggestions for picking a suitable map projection.  How accurate a scale bar would be on something like South America depends entirely on the chosen projection. 
FT3 can export a scale bar in the CC3 version of the map. That scale bar is valid only for the precise center of the map, however.
FT3 doesn't offer an on-screen scale bar, but it does have an information window that will show the visible extents of the screen area measured across the middle and center of the display.

----------


## Elros

> http://desktop.arcgis.com/en/arcmap/...F-FC70BE1F7E8D offers suggestions for picking a suitable map projection.  How accurate a scale bar would be on something like South America depends entirely on the chosen projection. 
> FT3 can export a scale bar in the CC3 version of the map. That scale bar is valid only for the precise center of the map, however.
> FT3 doesn't offer an on-screen scale bar, but it does have an information window that will show the visible extents of the screen area measured across the middle and center of the display.


What is the most commonly used projection in the fantasy maps on books? Equirectangular as i have undstand, right?
Using that projection, how much are the the imprecision?


How can i set the scale in photoshop when i have imported the map from FT  :Surprised:  ? I mean, how can i visually set the layer?

Maybe is not much important the scale but i want give at the readers an idea of map size.

----------


## waldronate

Most fantasy maps that I have seen don't specify a projection because it usually isn't important to the story. Equirectangular is a horrible projection because its distortion is 1/cos(latitude), meaning that it's literally infinite distortion at the poles. If you're not drawing a latitude/longitude graticule on your map, you can assume that it's in a projection that's flat enough for storytelling purposes.

The simplest way to give users a sense of scale is to use a scale bar on the map, even if it's not precisely correct. The simplest way to ensure scale transfers from FT to something line Photoshop is to draw a rectangular island or two of known size off of one or more coasts. Then mask out those islands in your final map using a legend or title layer.

----------


## Falconius

Most fantasy maps use no projection at all, not out of any particular thought but rather it's just easier that way.  ie, their maps occur 1x1 as if the world was flat. and then they sort of stick it like a post it on their globe if they later expand their setting.  The only fantasy world I can think of that this would actually work for is Discworld, but I don't think it's something one needs to worry about really.

----------


## Elros

> Most fantasy maps use no projection at all, not out of any particular thought but rather it's just easier that way.  ie, their maps occur 1x1 as if the world was flat. and then they sort of stick it like a post it on their globe if they later expand their setting.  The only fantasy world I can think of that this would actually work for is Discworld, but I don't think it's something one needs to worry about really.


So i can create my own world, then isolate one continent and i dont have to worry about projection?

----------


## Elros

> Most fantasy maps that I have seen don't specify a projection because it usually isn't important to the story. Equirectangular is a horrible projection because its distortion is 1/cos(latitude), meaning that it's literally infinite distortion at the poles. If you're not drawing a latitude/longitude graticule on your map, you can assume that it's in a projection that's flat enough for storytelling purposes.
> 
> The simplest way to give users a sense of scale is to use a scale bar on the map, even if it's not precisely correct. The simplest way to ensure scale transfers from FT to something line Photoshop is to draw a rectangular island or two of known size off of one or more coasts. Then mask out those islands in your final map using a legend or title layer.


So i dont have to worry about projection, right?
Ok i will try to do what you say on FT demo to export the scale in photoshop.
I dont have any question, you solved me all my problems  :Very Happy:  .


Thanks again for everything, really thank you. 
If i have problem or something to ask about FT, can i ask to you?

----------


## waldronate

I'm always happy to answer questions.

The only reason that you would want to worry about projection is if your area of interest is large and you want to use it's default measuring tools. If you are willing to declare that your world is planar rather than spherical and want to use ft, set ft to planar mode and never worry about projection issues again.

----------


## Elros

> I'm always happy to answer questions.
> 
> The only reason that you would want to worry about projection is if your area of interest is large and you want to use it's default measuring tools. If you are willing to declare that your world is planar rather than spherical and want to use ft, set ft to planar mode and never worry about projection issues again.


I cant declare my world is flat, i designed a story for a spherical world.
Can i make difficult measurements on FT?

I don't think i need long measurements, but if i need them, how could i solve the problem?
I have an idea, can i approximate long distances?
Writing something like "_they traveled in that sailer for about two months_".
Imagining 6-8 knots of speed, a 15-20miles at day, will be about 600miles in two months (I am approaching the miles at day of a boat at random).
I can?

In this case, how could i miss the measurement? Of months or days?

----------


## waldronate

FT's measurement tool provides distances in miles or kilometers (plus net change in degrees latitude and longitude, which isn't particularly useful for anyone). You can chain together multiple measurement segments by holding down the shift key to add a new segment. To get distance in units other than miles or kilometers, you'll need to do the math yourself to convert from the provided distance units to your preferred units. Similarly, if you want a non-constant travel cost (e.g. 5km/day in mountains and 20 km/day on plains), you'll need to measure each segment separately and apply appropriate cost per segment via an external tool such as a calculator.

Why doesn't FT do this sort of thing? Nobody asked for it (or not recently). The UI is also a bit complex because users would need to be able to specify what they're trying to measure and have some way to set up the various costs. Some users would undoubtedly ask for a way to store and recall paths to measure distances in different seasons (seasons are another thing that FT doesn't directly support). There are many possibilities for this sort of tool, but FT only provides simple distance measurement at the moment.

----------


## Elros

> FT's measurement tool provides distances in miles or kilometers (plus net change in degrees latitude and longitude, which isn't particularly useful for anyone). You can chain together multiple measurement segments by holding down the shift key to add a new segment. To get distance in units other than miles or kilometers, you'll need to do the math yourself to convert from the provided distance units to your preferred units. Similarly, if you want a non-constant travel cost (e.g. 5km/day in mountains and 20 km/day on plains), you'll need to measure each segment separately and apply appropriate cost per segment via an external tool such as a calculator.
> 
> Why doesn't FT do this sort of thing? Nobody asked for it (or not recently). The UI is also a bit complex because users would need to be able to specify what they're trying to measure and have some way to set up the various costs. Some users would undoubtedly ask for a way to store and recall paths to measure distances in different seasons (seasons are another thing that FT doesn't directly support). There are many possibilities for this sort of tool, but FT only provides simple distance measurement at the moment.


It's not a problem to make those that measurements by hand.

But if i have to travel in all the world in a great distance as in the example above. How wrong would it be?

Example:
Suppose i have to travel north starting from the equator, and i say that a month of travel by ship is 600 miles, from point A to point B, is it possible that B is a month farther or closer than i think?
If yes, how much am i doing wrong? An acceptable term?

----------


## waldronate

If head precisely north and south from the equator, scale doesn't change on a cylindrical projection like Equirectangular, so you're good. As you start to move east and west, though, the effects of projections start to come into play. The angular shrinkage east and west compared to north/south is proportional to cos(latitude), so at 25 degrees latitude (=111km/deg*25deg=2775km, the same number of degrees east and west is 90% of the size that it would be at the equator (94% at 20 degrees=2220km, 97% at 15 degrees=1665km). For a 600 mile trip near the equator, a straight line is probably a good enough approximation.

There are a number of useful calculation that relate distances on a sphere. Ed Williams' Aviation Formulary ( http://edwilliams.org/avform.htm ) lists many common formulae that might be of use to you. From that page: The great circle distance d between two points with coordinates {lat1,lon1} and {lat2,lon2} is given by: d=acos(sin(lat1)*sin(lat2)+cos(lat1)*cos(lat2)*cos  (lon1-lon2)).

----------


## Elros

> If head precisely north and south from the equator, scale doesn't change on a cylindrical projection like Equirectangular, so you're good. As you start to move east and west, though, the effects of projections start to come into play. The angular shrinkage east and west compared to north/south is proportional to cos(latitude), so at 25 degrees latitude (=111km/deg*25deg=2775km, the same number of degrees east and west is 90% of the size that it would be at the equator (94% at 20 degrees=2220km, 97% at 15 degrees=1665km). For a 600 mile trip near the equator, a straight line is probably a good enough approximation.
> 
> There are a number of useful calculation that relate distances on a sphere. Ed Williams' Aviation Formulary ( http://edwilliams.org/avform.htm ) lists many common formulae that might be of use to you. From that page: The great circle distance d between two points with coordinates {lat1,lon1} and {lat2,lon2} is given by: d=acos(sin(lat1)*sin(lat2)+cos(lat1)*cos(lat2)*cos  (lon1-lon2)).


Is a bit difficult to undstand the advanced mathematics of which you speak. 
Can you explain it to me a little easier?
So ifi move diagonally, can i run into a serious measurement error?

----------


## waldronate

You can largely ignore distortion for areas within 2000 km or so of the equator on an equirectangular projection. That information is important because it's image import needs its inputs in the equirectangular projection.

----------


## Elros

> You can largely ignore distortion for areas within 2000 km or so of the equator on an equirectangular projection. That information is important because it's image import needs its inputs in the equirectangular projection.


I understand, but there is no way to remedy this problem?
I had decided to set my story in an area far enough north or south of the equator to have a cold and cold climate.
How can i make measurements in such an area?
I think the only solution is to ignore the rules of reality.

----------


## waldronate

If you're only interested in distances and your area of interest is less than 4000km across, importing that are into FT along the equator will let FT treat it as if your flat map is in a form that FT can understand (i.e. the Equirectangular projection). You're not saying that it's not cold. It's just that for convenience of measurement, you're treating your map in a way that makes it easy to import and measure in a specific tool (FT in this case). Using FT isn't the important part here: putting your map at the equator lets you conveniently ignore the projection when importing the image into FT.

If you have drawn a map that's just a few thousand km across, you can declare that it's in a projection that is "flat enough" to use a regular ruler on it and you'll likely get less than 10% measurement error (10% measurement error is probably less than the error in the original cartographer's survey for most medieval-level fantasy settings). If you later want to paste that map onto a globe, then you'd need to declare what that projection and center of projection are. If you want to use FT as a tool for measuring distances on such a map with that map positioned on its correct place on the globe, you'd need to reproject the base map to an Equirectangular map so that FT can properly measure distances. It's not hard to do, but might well be beyond what you need at this time ( http://fracterra.com/ReprojectImage.zip is a program that will let you graphically reproject an image in a number of projections back onto the Equirectangular image that FT wants ).

I hope that make sense. My earlier recommendation to put your map at the equator was purely to make it easy to import into FT. Being more correct with measurements FT requires more complexity in putting the map into FT.

----------


## Elros

> If you're only interested in distances and your area of interest is less than 4000km across, importing that are into FT along the equator will let FT treat it as if your flat map is in a form that FT can understand (i.e. the Equirectangular projection). You're not saying that it's not cold. It's just that for convenience of measurement, you're treating your map in a way that makes it easy to import and measure in a specific tool (FT in this case). Using FT isn't the important part here: putting your map at the equator lets you conveniently ignore the projection when importing the image into FT.
> 
> If you have drawn a map that's just a few thousand km across, you can declare that it's in a projection that is "flat enough" to use a regular ruler on it and you'll likely get less than 10% measurement error (10% measurement error is probably less than the error in the original cartographer's survey for most medieval-level fantasy settings). If you later want to paste that map onto a globe, then you'd need to declare what that projection and center of projection are. If you want to use FT as a tool for measuring distances on such a map with that map positioned on its correct place on the globe, you'd need to reproject the base map to an Equirectangular map so that FT can properly measure distances. It's not hard to do, but might well be beyond what you need at this time ( http://fracterra.com/ReprojectImage.zip is a program that will let you graphically reproject an image in a number of projections back onto the Equirectangular image that FT wants ).
> 
> I hope that make sense. My earlier recommendation to put your map at the equator was purely to make it easy to import into FT. Being more correct with measurements FT requires more complexity in putting the map into FT.


Good  :Surprised:  ,this applies to maps smaller than 4000km. So most of my problem are solved i think  :Very Happy:  .




> If you later want to paste that map onto a globe, then you'd need to declare what that projection and center of projection are. If you want to use FT as a tool for measuring distances on such a map with that map positioned on its correct place on the globe, you'd need to reproject the base map to an Equirectangular map so


Do not risk distorting the image?
That is if I take a continent from an equirectangular projection, I edit it with photoshop, if I then paste it into the FT and declare it equirectangular again, don't I risk distorting it even more?

What if i had to draw a half-hemisphere route?

Thanks, you are really kind  :Very Happy:

----------


## waldronate

If you want to go from FT to Photoshop and then repeat that a few times, there will absolutely be an amplification in the distortion at every round trip. If, however, you are using FT to measure elements done in a Photoshop map, you can use the map in FT without worrying about distortion too much as long as you keep to the limitations discussed earlier. The idea of keeping your maps small and putting them near the equator for measurement is that you can safely ignore projection issues when measuring distances. Doing other things with the map will require you to pay attention to things that had been able to ignore in the simple case.

If you want to import a large section of your world into FT, then you will very much need to worry about distortions in your maps. You will need to be aware of the projection for your input data and then convert that data to Equirectangular for use in FT. That topic is a little more complex and would take a bit more discussion to resolve, I think.

----------


## Elros

> If you want to go from FT to Photoshop and then repeat that a few times, there will absolutely be an amplification in the distortion at every round trip. If, however, you are using FT to measure elements done in a Photoshop map, you can use the map in FT without worrying about distortion too much as long as you keep to the limitations discussed earlier. The idea of keeping your maps small and putting them near the equator for measurement is that you can safely ignore projection issues when measuring distances. Doing other things with the map will require you to pay attention to things that had been able to ignore in the simple case.
> 
> If you want to import a large section of your world into FT, then you will very much need to worry about distortions in your maps. You will need to be aware of the projection for your input data and then convert that data to Equirectangular for use in FT. That topic is a little more complex and would take a bit more discussion to resolve, I think.


I understand, in case i need long journeys I will look for a narrative expedient.
Thank you so much again for your time.
You were really kind, I will try to limit the damage from distortions trying to remain vague on the measurements, if as you said you, the damage of distortions is only 10%, is acceptable.

----------


## waldronate

I'm glad that I was able to be of some assistance. FT is one possible solution for the things that you said that you want to do and there are (as others said) other tools that can be used to get the same results. Best of luck with your measurements and feel free to keep asking any cartography-related questions here on the guild.

----------


## Elros

> I'm glad that I was able to be of some assistance. FT is one possible solution for the things that you said that you want to do and there are (as others said) other tools that can be used to get the same results. Best of luck with your measurements and feel free to keep asking any cartography-related questions here on the guild.


Thank you very much, if I need any more advice I will certainly ask.
Thanks again for your time  :Smile:

----------

