I've just started the very basics of a turn-based conquer-Earth type game. I plan to divide the Earth up into territories ala Risk. What's a good system for doing this? I could: 1. Divide the world into a rigid grid 2. Have 'shaped' territories via a masking texture and lookups on mouse clicks 3. Some other madness?!? Some additional, but less necessary info: I was thinking that I'd like to have the entire world shown on-screen at once, but this isn't yet set-in-stone. I'd like it to look fairly like Earth. This game will be pretty casual, as far as turn-based world domination games go (I'm thinking it would take at most an hour for one game, total. No 8 hour marathons like Civ or anything). I'm trying to keep this relatively simple. I'd like to finish a 'real' game for once. I'm surprised I'm struggling with this. It seemed easy to begin with, but it's one of those decisions that are causing me to have a constant battle with myself in my head. I just can't figure it out! Please, someone swoop down with the answer and save my day. And if you happen to have a handy map of the Earth suited for this (no labels, decent resolution, no political boundaries), I'd love to have it. No particular projection. Thanks in advance.

I think NASA Blue Marble has probably the best looking images (and a friendly license):
http://visibleearth.nasa.gov/view_set.php?categoryID=2355

How you can find the clicked upon territory is a good question; I'd say it depends on how complex they are (would approximating with bounding boxes be good enough?; most likely not).
Are you planning on creating the boundaries manually?

Maybe you could do a 'point in polygon' lookup; as it only happens on click that might be fast enough. Or you do some preprocessing (out of game) and use (for example) the (texture carrying) tile coords for a first phase to speed things up (and then only check the polygons that touch that rectangle; data from preprocessing).

If you try something like that the GSHHS data http://www.soest.hawaii.edu/wessel/gshhs/gshhs.html might even be a good source for the territory data; even the low/crude resolution should be fine.

Those Visible Earth images are perfect! And they have great Terms of Use, too.

Bounding box would be OK only if none of the bounding boxes overlapped - but that would happen unless I divide it up into a specific grid, rather than just arbitrary shapes (eg: compare Civ to Risk).

Another option: give each territory a 'capital' and instead of you clicking on the territory, you click on the capital. Pretty simple to implement, and would work well. What do you think?

go with masking. I've done it before and it works well.