It contains a map that shows the 4G LTE mobile coverage areas of the nation’s four largest mobile wireless carriers: AT&T Mobility, T-Mobile, UScellular, and Verizon.
It states that the coverage map was created using data submitted voluntarily by the four mobile carriers and depicts the coverage a customer can expect to receive when outdoors and stationary.
I am an AT&T wireless customer and have always found that cellular coverage varies significantly in the Memphis metro area.
This tool supports that experience on AT&T but I am skeptical of the other carriers' reporting.
Here is an example of LTE data in a neighborhood in Memphis that is not friendly to cellular towers.
Who do you believe?
For reference, here's a map of cell tower locations.