GIS5935 - Lab 8 - Surface Interpolation

Hello,

In the 2nd part of this lab we used different surface interpolation methods to estimate water quality in Tampa Bay.  We were provided data from 41 observation points where water quality samples were taken.  It is important to understand your data; where is it sparse or dense, where are there irregularities, and redundancies and use this knowledge to explain trends.  You may need to remove outliers and normalize data prior to applying an interpolation method.

To estimate the water quality of Tampa Bay we compared four different techniques, Thiessen, IDW (Inverse Distance Weighted), Spline Regularized and Spline Tension.

The Thiessen interpolation method provided more information about the data you are working with.  Any location within in a Thiessen polygon is “closer to its associated point than to any other point input feature.”  Using Thiessen interpolation I think is similar to creating a Voronoi Map in Geostatistical Analyst.  The disadvantage to using this technique is that when you assign each location within the polygon the same value as the nearest point, you could over generalize your data and not account for differences despite them being closely located together.   

The IDW method estimates cell values by averaging the values of the sample data in the neighborhood of each cell.  The closer a point is to the center of the cell being estimated the more influence or weight it has in the averaging calculation.

There are two Spline methods: Regularized and Tension.  The regularized method creates a smooth, gradually changing surface but may have values that lie outside the range of the sample/input data.  The tension method controls the stiffness of the surface based on the input data but creates a less smooth surface with values constrained by the range of the sample/input data.

I've chosen to display my Spline with Tension Interpolation of the water quality in Tampa Bay as I felt it was the best method to estimate water quality based on the data we were provided via the 41 sample locations.

Spline with Tension Interpolation Method