Shaders and Texturing - An Introduction to Computer Graphics for Artists - page 209

Fig. 11.33 In this blend map, each of the three primary colors corresponds with one of the three
base maps (Image courtesy of Lennart Hillen)

Fig. 11.34 The combination of a blend map and the three base maps yields irregular blended
boundaries between base maps (Image courtesy of Lennart Hillen)

11.5.7 Relationship of Textures and Model Construction

The way you plan to texture your model will affect the way the model is built. If you
intend to use normal maps, you will need to build two versions of the geometry: low
resolution and full resolution. If you use tile sets, you will position texture boundaries
differently than if you use the tiling or non-tiling texture method. If you use transpar-
ency to replace geometry with a texture map, such as an iron fence, you might want to
build the fence as geometry and make maps from the geometry, or paint it as an image.