[Award Winner] Using tectonic plates to draw a world map

[dhalsimrocks]

I looked through all the other threads in this forum and didn't see anything related to it, so I thought I'd make my very first post here a tutorial.

WARNING - This tutorial gets somewhat technical

If you're anything like me (a science geek), your fantasy worlds have to be based on some degree of scientific fact, rather than total randomness. I've been working on a fantasy world for going on 13 years now, and I lost the original world map I had drawn. So I recently found myself thinking of making a new one from scratch.

Having learned about the prehistoric supercontinent, Pangea, many years ago, I thought about creating my new map by drawing a supercontinent and imagining how it would break up and form my world map. I researched previous supercontinents of Earth, such as Pangea, Laurasia, Gondwana and even older, Rodinia. Eventually, my research took me to geological basics: tectonic plates.

I then realized my method would not be in creating a fictional supercontinent and breaking it up, but by determining the existing tectonic plates of my fictional world and letting them decide what it would look like, along with a little deliberation on my part. The end result was pleasantly surprising. Now, on to the "How".

Step 1 - Drawing the Tectonic Plates

Note - please read the entire tutorial before proceeding with this step.

As a point of reference, examine the Earth's tectonic plates:

http://en.wikipedia.org/wiki/Imagelates_tect2_en.svg

Keep this open as I'll be referring to it later in this guide.

Notice that there are 7 large, major plates and 8 small, minor plates (there are actually more minor plates, but for all intents and purposes in this guide, we'll say 8 ). Also notice that their shapes are not very erratic. There are very few inward curves.

So start by drawing a similar number of large and small plates. This is a very easy step, actually. Just as in the photo of the Earth's plates, the borders do not need to have a lot of randomness, like a coastline would. And keep in mind that the shape of the tectonic plate does not necessarily determine the shape of the continent (but it can).

The next step is to determine the direction of the plates' movement. This page shows the general movement direction of Earth's plates:

http://education.sdsc.edu/optiputer/...lateArrows.htm

Notice that there is a mix of directions. You should try for a similar mix. These plate directions will be a large influence on the terrain of your final map, so use some deliberation here, but make a few of them random (whatever direction comes off the top of your head) to make things interesting.

Here is an example of the plates and their directions for the map I recently worked on:

tectonic_plates.png

Before we continue, I will need to digress and give a basic geology lesson.

[dhalsimrocks]

Digression - Basic Tectonic Plate Geology

The movement of Earth's tectonic plates has an enormous effect on its terrain. Most important to this are the boundaries of the plates, and there are two factors that come into play: the type of crust at the boundaries and the type of boundary.

There are two types of crust: oceanic and continental. Oceanic crust is exactly that: crust that forms ocean floors. Continental crust is that which creates landmasses, although not all continental crust is above water.

There are 3 types of plate boundaries:

Transform boundaries, where two plates slide past each other (rub the palms of your hands together for a visual aid). California's San Adreas Fault is an example of a transform boundary. Transform boundaries produce many earthquakes.

Divergent boundaries, where two plates are moving away from each other, creating oceanic ridges and continental rifts. The Atlantic Ocean was produced by divergent plate boundaries between the North American + South American plates and the Eurasian + African plates. They were once joined together in the Pangea supercontinent, but the plates movement spread them apart and the divergent boundary created an ocean. Africa's Great Rift Valley is also being caused by a divergent boundary.

Convergent boundaries, where two plates are colliding. This creates mountains and/or oceanic trenches or island chains, depending on the types of crust that are colliding. Convergent boundaries create a process known as "subduction", where the crust of one plate slides underneath the crust of the other. This creates volcanic activity along the line of subduction. This will be important later.

Transform boundaries have a lesser impact on terrain than divergent or convergent boundaries, although it is important to remember that they do cause earthquakes!

Divergent boundaries occur between two continental crusts or two oceanic When two oceanic crusts meet at a divergent boundary, it creates an oceanic ridge, not to mention new crust. These are basically crust formation points, and you should have one or two on your map. Example: The Mid-Atlantic Ridge.

When two continental crusts diverge, you get a rift valley, and over time, they separate into two landmasses. Example: Africa's Great Rift Valley.

Convergent boundaries between two oceanic crusts eventually create chains of islands (usually in an arc). The subduction causes volcanic activity that eventually builds up into islands. Examples: Aleutian islands, Phillipines.

Convergent boundaries between oceanic crust and continental crust creates volcanic mountain ranges on the edge of the continental crust, because of subduction. Examples: Andes Mountains in South America, Cascade and Sierra Nevada mountains in the USA.

Convergent boundaries between continental crusts creates dramatic mountain ranges as the landmasses smash into each other and buckle the landscape. One crust can subduct beneath the other. The classic example is The Himalayas. This was caused when the Indian Plate crashed into the Eurasian Plate at a high rate of speed (still very slow, however). The Indian Plate is slowly subducting beneath the Eurasian and is creating the tallest mountains in the world, as well as the Tibetan Plateau (the highest in the world).

For a visual of most of the scenarios:

http://en.wikipedia.org/wiki/Image:T...boundaries.png

Also, see the image of the Earth's plates.

So now that we know how the different boundaries and crusts effect the landscape, we can take the next step in producing our map.

[ravells]

This is a very interesting and educational read! Thank you very much for posting! (I'll delete this message after a few days so as not to interrupt the flow of your tutorial).

[jfrazierjr]

Thanks for the info AND the links. Though I will proabaly not delve this deep, it is nice to have an idea of what might be going on in the real world. I think for me, this will mainly help influence the idea behind why islands are where they are and how many of them there are.

I know some people over on the NBOS forums have had some debate about how most mapping programs that generate worlds don't take this into account and the general thing is that you would need hugh housepower or tons of time to even approximate getting this created right. Mainly, this is directed at Fractal World Explorer or Fractal Terrains autogeneration functions. For the most part, the people on that forum are fairly agnostic in how real geology affects world creation. Most people have the attitude (which I mostly have) that "its just a fantasy world, so as long as the rivers go down hill, thats probably good enough for me."

Joe

[dhalsimrocks]

Step 2 - Drawing the Continental Crust

It is now time to decide where the continents will be and give them their shapes.

When I did this, I made a few copies of the tectonic plate sketch on which to draw my continents and landmasses.

But where to start?

One good place would be to find your divergent boundaries. This is a possible location for an oceanic ridge/crust formation point. This is also a possible location for two continents that were one time joined together, but are now separated, like South America and Africa. So you might want these two continents to have coastlines that would mostly "fit together", but separated by a body of water.

Once you have those coastlines drawn, think about the rest of the continent. The shape can be entirely up to you and can have a lot of randomness.

Next, think about your Oceanic Plates. When looking at the Earth's plates, you will notice that only two major plates have no continental crust at all: the Pacific Plate and the Nazca Plate. One of your large plates could be entirely oceanic, and would therefore be a location for one of your oceans, if not the largest. It would also be a good location for a "Pacific Ring/Ring of Fire" type scenario, where most of the plate's boundaries have a lot of volcanic and seismic activity, not to mention some of the deepest trenches where there is the most subduction.

Then look at your convergent boundaries. They will be the locations of either Himalaya type mountain ranges, Andes or Cascade volcanic mountain ranges, or volcanic island arcs. Decide what you would like to have and where. This can help you decide where your oceanic and continental crusts will be.

Finally, think about whether or not you want any continental divergent boundaries, where there may be a large rift in the continent (and a new plate boundary forming).

Most of this step is up to you, but is also largely determined by how you drew your tectonic plates and what direction they are moving. Take some time with this step and make it your own.

Here is what my map looked like after adding the continents (it's not the finished product):

continents_plates.png

Continents A and B are separated by an ocean created by a divergent plate boundary. They were once together and as such, they would "fit" if placed side by side. Both would also fit with the southern continent, which I forgot to label, as that is also a divergent boundary.

A<->G, E<->B, F<->D and C<->D are all continental convergent boundaries and are creating large mountain ranges.

Notice the island arcs between all of the oceanic convergent boundaries.

All the way to the north is a continental rift caused by a continental divergent boundary. (x) will one day be its own landmass and tectonic plate.

The island between G and (x) has a ridge of mountains caused by a convergent boundary and subduction. B has one as well, but that's from a very old subduction that is not current.

Now, I'm sure a legitimate geologist would look at this and tell me a thousand little things I did wrong, but it has enough scientific base for me, and it has resulted in a realistic looking map. And what's more is that there was enough randomness involved that I didn't know exactly what it was going to look like in the end, so it was just a bit of a surprise.

I still have some more work and detailing to do before going on to editing this in the GIMP according to RobA's excellent guide.

Anyway, even if you don't use this whole method to create world maps, I do hope that there is information here that could be helpful in determining at least some of the terrain on your maps or help shape continents.

Thanks for reading!

[RPMiller]

I looked through all the other threads in this forum and didn't see anything related to it, so I thought I'd make my very first post here a tutorial.

Post #14 in this thread.
http://www.cartographersguild.com/sh...hlight=predica

I will definitely be reading through this thread with great interest. Thank you very much and have some rep! Oh, and Welcome to the Guild!

[Karro]

In my worldmap, I'm using largely the same approach. I had a few basic ideas about where I wanted continents to go, and a few shapes I wanted to use based on some old maps I had done as a child, but mostly I wanted to fashion the world from scratch using some basic understanding of plate tectonics.

I'll be working on this more after I finish my little side-jaunt learning how to use GIMP.

[Redrobes]

Well done - this is shaping up to be a great thread and read. Keep it up ! Have some more rep...

[HandsomeRob]

It may be important to remember that plate motion can't really be described by simply drawing an arrow on the plate and saying "it moves that way." Actual plate motion is actually a rotation around a point on the earth's surface. What you really need to know for this exercise is relative motion; it is completely possible to say that plate 1 is moving west (with respect to plate 2) and at the same time moving east (with respect to plate 3). This situation happens all the time.

Here is a quick tutorial on velocity space analysis:
Say you have a situation like in the first attachment here. Plates A and C are moving toward each other at a rate of 4 cm/yr. Plates A and B are moving away from each other at a rate of 3 cm/yr. What is the motion between plates B and C?

Construct a velocity space diagram to find out (see second attachment). Since plate B is moving west at 3 cm/yr (with respect to plate A), place a point for B 3 units to the west of A. Since plate C is moving south at 4 cm/yr (again, with respect to plate A), place a point for C 4 units to the south of A. Now it should be clear that plate C is moving southeast at 5 cm/yr with respect to plate B, as the point for C is 5 units to the southeast of the point for B.

This means that the B/C boundary is convergent, with an element of right-lateral strike-slip motion as well. The third attachment here shows the solution.


I hope some of that a) makes sense and b) helps.
-Rob

[dhalsimrocks]

It may be important to remember that plate motion can't really be described by simply drawing an arrow on the plate and saying "it moves that way." Actual plate motion is actually a rotation around a point on the earth's surface. What you really need to know for this exercise is relative motion; it is completely possible to say that plate 1 is moving west (with respect to plate 2) and at the same time moving east (with respect to plate 3). This situation happens all the time.

Excellent information to add to this! Thanks! The plate tectonics rabbit hole goes pretty deep if you really get into it. And there is a lot more that what I said to be considered if you want total accuracy. (which is precisely what I meant when I said a legitimate geologist could find a thousand things I did wrong. )

I initially entertained the thought of taking the rotational motion into consideration, but my desire to have a new map overtook my desire for scientific accuracy, and decided that it would add considerable complexity, and thus time, to my project. So that's why I stopped at the point of drawing an arrow on the plate and saying "it moves that way".

I take that back, I did take rotational motion into consideration for a few of the plates on my map, but I didn't note it. In particular, my southernmost plate is rotating anti clockwise.