Agustin B. Graterole Adv. GIS Lab 11: Interpolating Continuous Surfaces April 25, 2009

I. Step 2 Maps

IDW vs. Spline Interpolation

According to the nature of the wet deposition process and the scale of the study area, I find

the most appropriate interpolator to use the Inverse Distance Weighted (IDW). When comparing the

spatial extent of the deposition of these chemicals to the large size of the contiguous U.S., it seemed

more appropriate to use an interpolation technique that wouldn’t assign value to a surface that

passes exactly through the data points in all the U.S. Also, the Spline interpolator produced negative

numbers which were never in the data inputted.

II. Step 3 Maps

II. Step 4 Maps

Location and Spatial Pattern of Wet Atmospheric Deposition on the U.S.

Areas of high deposition of ammonium occurred mostly on the northern portions of the Midwestern and

Central U.S. in both 1985 and 2007. These areas are characterized by a large presence of farming and some

industries. The use of fertilizers in large amounts on agricultural areas may be a large contributor for causing

ammonium deposition. Ammonium deposition increased on these north-central agricultural areas of the U.S

between 1985 and 2007. Meanwhile areas where it decreased were located on some south-eastern states and

northern portions of Michigan and California.

Areas of high deposition of sulfate on 1985 occurred mostly on the Midwestern and Northeastern U.S.

where a large amount of active industries existed. By 2007 a lesser amount of industries were active in these

regions and therefore the amount of sulfate deposition decreased. However, the central and south-central part of

the U.S. showed a widely increase in deposition. The western part of Virginia and North Carolina featured a

significant increase but not smaller in terms of its spatial extent.