How To Use the Memphis Hazard Map Data
Creating a Surface from Points
The surfaces created for the maps in the Graphical Format section were produced by interpolating the point shapefiles that are available for download on this site.
There are several methods of interpolation available in Spatial Analyst and a brief description is provided below. More information is available in ArcGIS Help.For this series of maps, spline interpolation was used.
A brief overview of the ArcGIS Interpolation toolsetSurface interpolation functions create a continuous (or prediction) surface from sampled point values. The continuous surface representation of a raster dataset represents height, concentration, or magnitude (for example, elevation, pollution, or noise). Surface interpolation functions make predictions from sample measurements for all locations in a raster dataset whether a measurement has been taken at the location or not. There are a variety of ways to derive a prediction for each location; each method is referred to as a model. With each model, there are different assumptions made of the data, and certain models are more applicable for specific data (for example, one model may account for local variation better than another). Each model produces predictions using different calculations.
The Inverse Distance Weighted (IDW) and Spline methods are referred to as deterministic interpolation methods because they assign values to locations based on the surrounding measured values and on specified mathematical formulas that determine the smoothness of the resulting surface. A second family of interpolation methods consists of geostatistical methods (such as Kriging), which are based on statistical models that include autocorrelation (the statistical relationship among the measured points). Because of this, not only do geostatistical techniques have the capability of producing a prediction surface, but they can also provide some measure of the certainty or accuracy of the predictions.
|The interpolated grids were then displayed by drawing raster stretching values along a custom color ramp.
Ramping colors in the Layer Properties dialog box:
To recreate the color ramp used in this map series, use the following fourteen algorithmic color ramps:
Or, download Memphis.style and place in C:\Program Files\ArcGIS\Bin\Styles. When you go to the Style Manager you will see Memphis on the list. Select it and it should then be available in the selection of color ramps in Layer Properties => Symbology => Stretched.
Then edit the high/low values for all data sets to 0.99 high and 0.01 low. Otherwise the colors will be stretched only through the range of the current data set rather than the range of all the datasets.