Standard set of symbols used by USGS in topographic maps. Schools, oil wells, mines, airports, swamps, have their own symbols. Most people can discern 1,000 shades, some can differentiate 1000,000 colors. Scale is important since details on maps must be generalized when moving from larger to smaller scales. The mathematical techniques called projection is used to convert locations on curved surface of the earth to corresponding points on a flat surface of a map.
Projection causes distortion of true shape, area or orientation of mapped features.
Locations are determined either in degrees, min. Latitude and longitude . Grids the earth with parallels and meridians . Divides each U.S. State into 1-10 zones and uses best projection in each. We are in Central Zone of 5 in Texas.