I've heard a lot about Terrain Bitmaps but don't really understand how or why they are used in map making. Can anyone explain?

You mean like Blood Gulch ground bitmap?

Exactly. All the default maps and some custom maps use this format of texturing the ground and whatnot. So how does one achieve this?

Its all about the shader. It's shader_environment and it can have 2 different detail maps like grass and sand. You can change where one and other appears in alpha channel of the texture.

in a layered terrain texture:

----the 'base map' is used to specify what color each part of the terrain should be(it really is that simple, try examining the bloodgulch terrain texture(blood ground))
--the 'alpha' in the base map determines where the 'primary detail' map should appear(and because it is alpha, the intensity of it too)

----the 'micro detail' map just appears everywhere... I think its intensity is controlled by the 'alpha' of the 'primary detail' map



This goes a long way too. The reason grass and dirt doesn't look like it tiles when you play bloodgulch or some other bungie-made map is because they're blended into terrain textures :)

Thank you all for your feedback. The community needs more people like you!