A blue line on a map usually represents a stream or other water feature. Blue lines and other symbols that stand for features of the Earth's surface are found on topographic maps.
Topographic maps use symbols and colors to represent what is found on the ground in a particular area in terms of elevation, vegetation, water bodies, roads and man-made structures. Blue is used to indicate water, green refers to trees and grass, topographic symbols are brown and black, and red represents buildings and other manmade objects .
Brown contour lines on a map show elevation of an area in feet above sea level. Bench marks indicate where the elevation was surveyed. Forests are shaded green on maps, while areas without forests are white. Roads and trails are represented by red or black lines, and their thickness indicates the quality of the road. Highways are shown as thick red lines, and double dashed lines stand for dirt roads. The thin single dashed lines are trails.
Maps show the outline of individual buildings and positions of structures such as radio towers. If the map depicts a large area, it might represent a densely built city as an area of pink. Combinations of dots and dashes on maps represent boundaries.