Pollution+erosion+model

=Pollution Erosion model=

Suggestions on improving the model from Shawn:
The approach to use it divide and conquer. As usual there are several approaches, but I will describe two here.
 * Topic: ** GEOS9016 **Date:** 6 May 2009 2:06 PM
 * Subject:** Re:Erosion model **Author: Shawn Laffan**

Version 1: 1. Buffer the relevant roads (select the ones you want and use them in the buffer tool).

2. Convert the result to a raster layer (remember the extent and cellsize should be the same as your other files)

3. Use the "is null" tool with the result of #2 to to generate a layer that has a value of 1 where there was nodata (i.e. where there was no buffer polygon) and 0 elsewhere (cells within the buffer).

4. Multiply ("times" tool) the raster with the values you want to mask by the result of #3. Anywhere that was near a road will now have a value of 1, all other locations will have their original value.

Approach 2: 1. Convert the roads lines to a raster (remember the extent and cellsize again).

2. Use the euclidean distance tool to generate a raster where each cell has a value of the distance to the nearest road cell.

3. Use the con tool with the distance layer, but set the first output (input true raster or value) to 0 and the second output (false raster...) to the layer you wanted to mask in the first place. The condition should be "Value < x", where x is your threshold distance.

The con tool can take a little getting used to, but it is one of the more powerful tools in the toolbox, as the output rasters/values don't have to have anything to do with the those used for the input conditions.

Let me know if more clarification is needed.

Shawn.