I think storing maps as images is quite common actually for simple games not made in a game engine that handles maps.<p>You can also use the drawn map as a template, and add random details (random variants of each tile). Also, you'll quickly find you want to use more sophisticated autotiling which handles multiple tile types meeting, and special cases. Here's an article about autotiling by defining rulesets which goes into more detail: <a href="http://www.squidi.net/three/entry.php?id=166" rel="nofollow">http://www.squidi.net/three/entry.php?id=166</a>
Well written, but as others have mentioned, this technique is almost as old and well-known as game development itself.<p>However, it's still pretty cool and refreshing to use. See e.g. Notch' Ludum Dare streams where he makes his levels in Paint.net: <a href="http://www.twitch.tv/notch/b/293084461" rel="nofollow">http://www.twitch.tv/notch/b/293084461</a> about 3:23:00 in.