near Denver might have index contours of 5,000', 5,100' and so on with a contour interval of 20 feet. This means that there would be five "spaces," and four non-index contour lines, between each index contour. Often, index points are given along with index contours.
because.... they had a constant supply of water. This means building cities and planting farms was much easier than it was in these places than others.
