How These Maps Were Created How to interpret the maps: These interpolated surface maps show an estimate of the average count of a species for a location. Increasing color darkness indicates an increasing number of birds. White denotes areas of no observations or insufficient data. How the maps were made (a technical summary): The maps are surface maps interpolated from the locations as inverse distance weighted averages using an influence radius of 100 kilometers and a power of -2 decay of influence. In other words, each point on the surface maps is the mean of all values with a radius of 100 kilometers weighted by the inverse of the square root of the distance to each point. The colors were selected for ease of perception.