1. what are the following colors used for on usgs topographic maps? green: blue: brown lines: red: black: salmon or gray: 2. define index contour. 3. how often are these lines shown on a map (usually in the us) 4. how are they represented…..what is done to these lines to make them stand out from the other lines? 5. define contour interval. 6. briefly describe in detail how a depression contour and a hilltop would be represented on a map. depression - hilltop-