Arkansas’s Hottest and Coolest Cities

Interpolation, Applied GIS with Dr. David Baylis, University of Arkansas at Little Rock, April 11, 2020

 The following maps show Arkansas’s hottest and coolest cities for the months of January and August as well as climate data for the major cities in the state using two different interpolation methods. Interpolation is a process that calculates a surface of estimated values based off a set of known values of a continuous variable. The first two maps use the Kriging interpolation method and the last two use the Inverse Distance Weighting (IDW) method. Kriging is an advanced geostatistical procedure that produces an estimated surface based on a set of points taking into account spatial relationships and distributions of variables. The IDW method on the other hand, is more simplistic method of generating an estimated surface. Cell values are estimated by averaging values of sample data points from the neighboring points. Points that are closer the center of the cell have more influence, or weight, in the calculation.

The results of these two methods of interpolation produced slightly different results. In maps 1 and 2 it is clear that the Kriging method produces more accurate results. It minimizes the bullseye effect that occurs with IDW interpolation in areas where there is a clustering of points. Comparing maps 1 and 3 we can see that Map 3 has more of these bullseye areas than the Kriging map which has a more natural distribution of temperatures. Kriging also generates areas that are more sharply defined as opposed to IDW which is overall more smooth. The temperature range varies slightly between interpolation methods. For example, in the month of January, the Kriging method generated a more narrow range of temperatures ranging from 35-43°F whereas the IDW method generated temperatures ranging from 33-45°F.