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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | GISList: Problem: Percent Impervious Values in Raster Grid |
| Date: |
05/06/2002 09:53:06 AM |
| From: |
Jon Caris |
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Hi Listers,
Here is my problem du jour.
Objective:
Create a raster grid with percent impervious land features (building and
roads)
Method:
1. Merge buffered roads and buildings into one layer [rdbldgbuf\
2. Generate a fishnet polygon grid [polygrid\ with 100 meter "cells".
Therefore, each cell has an area of 10,000sq meters.
3. Erase [polygrid\ with [rdbldgbuf\ to calculate a new layer
[prctimper\ with an attribute for percent impervious - X sq. Meters /
10,000 sq m = %impervious.
4. Create centroids from [polygrid\ to create centroid layer [centroids\
5. Run Identity on [centroids\ with [prctimper\ to transfer % impervious
attribute to centroids
6. Create raster grid from [centroids\ using area as grid value
Problems:
Both ArcMap and ArcView are bombing out during the erase operation.
ArcView actually gets half way. ArcMap goes nowere. The
layers are not terribly large [rdbldgbuf\ = 1,000 polys: [polygrid\ =
500 polys.
Running workstation arcinfo does the erase, but converting [rdbldgbuf\
from a shapefile to a coverage creates large polygons between loops of
buffered road. So, erase removes too much area from the fishnet grid.
I'm open to solutions using my methodology or an entirely new
methodology. Will sum and thanks in advance.
Jon
Jon Caris
Spatial Analysis Lab - Bass 105
c/o Clark Science Center
Smith College
Northampton, MA 01063
voice: 413 585 3597 fax: 413 585 3786
http://www.science.smith.edu/departments/sal
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