Since topographic contours represent points of equal elevation, the contour elevation tells you the elevation difference between two adjacent contours. Generally, contour intervals are in units that allow you to see the elevation differences. Larger contour intervals are typically used in regions with large differences in elevation (e.g., mountainous regions) conversely, regions of very small topographic relief (e.g., coastal plains) will have a smaller contour interval to show more detail. On USGS , every 5th contour is usually shaded dark brown.