Dungeons are underground. Maps display the surface. Therefore, dungeons do not show up on maps.
If a dungeon is underground, it will not show on the map. If is collapsed in a desert, it will show up as a slightly darker square of yellow.
They randomly generate throughout the world, to find one just keep digging underground.
a map's scale shows the population of minecraft
the color blue on a map often shows a lake or an ocean = D
Mountains are usually brown on a map.
If you're talking about a Minecraft world, there is no limit. The world keeps randomly generating. If you're talking about the map item, it changes. As of 1.4 you can expand a map to make it show more blocks.
green
blue is the color that shows most on a map.
Green.
Brown...
[object Object]
It depends on your map, but green is usually the default color for fertility.