Get your free Wall-Sized Map of Effective Ground

Click to enlarge (This is not the wall size map, see below for link)

Ground conductivity plays a major part in the effectiveness of your Part 15 AM broadcast range (or any other type of AM broadcast). Knowing the ground conductivity of your particular area is a useful indicator to determine what level of signal performance to expect.

Via the FCC you can download a high resolution ground conductivity map broke up in 48 parts to optimize for printing on multiple 8 1/2 inch by 14 inch papers and assembled to the full size 43 x 69 inches map. Free download available at: http://www.fcc.gov/encyclopedia/m3-map-effective-ground-conductivity-united-states-wall-sized-map-am-broadcast-stations
 Here's an example of one part of the map:

Map of Effective Ground Conductivity in the United States (A Wall Sized Map), for AM Broadcast Stations

 Figure R3 of 47 CFR 73.190 of the Commission’s Rules contains a map of the estimated effective ground conductivity in the United States. This data is used to predict the propagation of AM signals across the United States. A higher ground conductivity indicates better AM propagation characteristics.  The map shows that the ground conductivity in the U.S. ranges between 0.5 and 30 millimhos (or millisiemens) per meter.  The conductivity of seawater is 5,000 millimhos per meter, resulting in the best propagation of AM signals.