Chicago's Grid System
Chicago is one of the easiest cities to get around in because of its grid system. The grid system provides a coordinate for wherever you are in the city beginning downtown at the corner of State (0 North / 0 South) and Madison (0 East / 0 West) and radiating outward.
From that point, every intersection is given a coordinate that corresponds to where you are in relation to the grid's origin (State and Madison). Each north/south street is labeled with a number indicating how far east or west of State street you are. Each east/west street is labeled with a number indicating how far north or south of Madison you are. For example, if you were at the corner of Armitage and Halsted, you would be 800 W (Halsted) and 2000 N (Armitage). For easy navigating, consult street signs at intersections; they usually identify the streets' grid coordinates.
To calculate distance, estimate that eight city blocks roughly equal one mile. Since each hundred is one city block, if you want to walk down Halsted starting at Armitage Avenue (2000 N) and stopping at North Avenue (1600 N), you will walk roughly four blocks, which equals about half a mile.