Distance Rings/Simple Buffers
Maps with distance rings (i.e., 1, 2, and 3-mile rings) are the simplest and most widely used method for defining a trade area. While they can be drawn from any point, the middle of a downtown is often the most appropriate point from which to create distance rings.
This approach can work for a quick analysis or for areas that have fairly uniform geography. For example, if you are defining a trade area for a small community surrounded by similarly-sized communities that are all spaced 20 miles from one another, a simple ring of 10 miles may be a reasonable trade area for analysis.
While rings are an easy method to use, they fail to recognize travel barriers, such as natural features (mountains, rivers, lakes, etc.) and man-made elements (road networks, etc.). Subsequently, rings are useful for only simple analysis.