# Mapmaking Discussion & Philosophy (WIP/Critique) > 3D modeling (map elements and height maps) >  Do you use ellepticity in your mapping?

## Rock

I've only just begun poking around in the various maps here, but I've already seen some absolutely beautiful work and attention to detail.  What really intrigues me is that there's a strong focus on tectonic action, geographic effects on weather patterns, topographic contours, etc..  It's what should be considered, yes, I just normally don't run into people who go that in-depth (I'm a math & physics nerd, so this grabbed my attention big-time).

That got me wondering.  Out of purely idle curiosity:
1) Has anyone here taken ellipticity into account in their mapping?
2) If you have, then did it make any significant difference in the results, their aesthetics, etc.?
3) Would you recommend for or against bothering with it -- and why / why not?

Ellipticity math reference: https://math.stackexchange.com/quest...of-ellipticity (please pardon the fact that the linked question's answer is my own, but it really does have the info. all in one spot, to include both fourth order flattening and fourth order eccentricity, which you just don't run into very much at all).

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## Falconius

We tend to use what we have at our understanding.  Making an accurate spheroid, (which is what I assume ellipticity has to do with, since even now I still don't understand exactly what it is) that is then projected flat seems a bit beyond the scope of useful consideration.  As in when drawing a map, which is flattened or in some way distorted for representation what are the practical effects of calculating ellipticity?  Is there any point.  Even for real world use for charts etc. would it have any practical measurable effect or point?  Unless you are talking about mapping extreme cases.

If this has nothing to do with spheroids just ignore me.  :Smile:

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## waldronate

The Earth's eccentricity is about 1 part in 300 along one axis away from being a perfect sphere, so it's frequently referred to as a spheroid. That's not enough for most people to notice when displayed at a reasonable size (the line thickness and projection will usually put in more visible distortion than the about 0.5% difference in position resulting from sphere / spheroid).

https://gis.stackexchange.com/questi...th-as-a-sphere does some computations to arrive at a maximum position error of about 22km (roughly 0.5%). For a 22" HD monitor (100 ppi), that's about 1/20 of an inch of difference maximum (and usually much less). Most folks that I've encountered wouldn't be able to generate data accurate enough for people to be able to register that level of difference.

For most hand-drawn maps of worlds made of low-strength internal materials that spin fairly slowly (that is, Earth-like worlds), this level of inaccuracy is invisible. As worlds get smaller or spin faster, though, they tend to get less spherical, but it doesn't usually get too bad very fast. Unless you're using GIS tools with relatively modern survey data (and whoever uses the resulting map actually needs that level of accuracy), the difference between a sphere and an ellipsoid for making maps is unlikely to matter to consumers of the map.

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## waldronate

If you're really into excessive amounts of math and physics, you probably would be interested in considering the shape of the gravity field (the geoid) rather than some abstract approximation of shape (the ellipsoid or spheroid). Understanding the geoid will help you to be able to answer two important survey questions: which way is up, and how high above sea level are you.

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## Azélor

https://www.google.ca/search?q=regul...AKDZLCaUCSq2M:

This?
This is an extreme example, just to see if we are talking about the same thing.

As Waldronate said, it is something marginal on most planets and the map distortions are much greater than the difference of not being a perfect sphere.

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## Rock

Falconius:  Yup, the spheroids reference is spot on to ellipticity.

waldronate:  I have studied the geoid before, and found it fascinating.  I pretty much figured that it probably wouldn't see much use in typical situations (flat or spheroidal mapping), but figured that I should ask anyway, to see if I'd maybe overlooked a surprising side-track possibility (you never know).

Az_é_lor:  Yup, that's it precisely. :-)

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