# What can be determined about an Earth-like planet, just by looking at a map?

I have a fictional map for an Earth-like planet, with Renaissance-era humanoid populations. Also, Luna, that is, the exact same moon that we had, pre-Space-Race, is orbiting the planet.

My map just has landmasses on it. No elevation markings, no forest markings, no desert markings... nothing but:

This place is land/ice (both look the same...), this place is sea.

What can I determine about my planet just from that map, if anything?

For example, could I tell where the poles/equator are?

• I think this is Question # 2,500. Commented Jul 11, 2015 at 20:00

Assuming the map is complete (ie. covers the entire planet from pole to pole) and uses a sensible projection, you can find the equator and poles geometrically: the edges that match up are east-west, the poles are the other two edges, and the equator runs down the middle between the polar edges. If the map isn't complete (it doesn't run to the poles, or it doesn't circle the entire planet), you can't determine the poles or equator.

You can find coastal mountain ranges and coastal plains: a "ragged" coast like that of Norway has a mountain range, while a smoother coast like that of China is evidence of a plain built up by river deposits.

If large lakes/inland seas are marked and you can tell north-south from east-west, you can identify a recent ice age by abundant lakes in the northern and southern land areas.

If the map is detailed enough, you can spot river deltas even in the absence of marked rivers; these are good places to look for civilization.

You can deduce plate tectonics and mid-ocean ridges from the shape of the continents; you may be able to deduce rift valleys and uplift mountains as well. From this you can figure out various things, eg. that Iceland is volcanic.

If you know where the equator is, you can figure out the prevailing winds, and make broad deductions about the climate (eg. a coastal range with a sea-to-shore wind will produce a rain shadow desert and a rainy/foggy coast).

• There are sensible projections that don't have matching west-east edges. Commented Jul 10, 2015 at 4:47
• @PyRulez, true and those are some really fun maps to look at. :) Commented Jul 12, 2015 at 4:19
• @Green I've even seen projections that tesselate (so borders become less problematic.) Commented Jul 12, 2015 at 4:45

Not much.

Without knowing the map projection, planet rotation, climate, elevation, atmospheric properties, or scale there isn't much you can determine at all. Basically, you might only be able to guess the poles and equator.

Poles
Even most Earth maps don't have the poles on them. The famous Mercator projection cuts off the map hundreds of miles before the poles because the distortion is so extreme. However, you might be able to guess at the planet axis by looking for symmetric ice formations. The power from the planet's star will likely not be as strong there, leading to colder areas.

Equator
It's between the poles! More specifically it would be mostly perpendicular to the gradient of not-ice to ice on the map.