[GRASS-user] aggregate a field across features and then display related charts and histograms

[Michael Barton]

On Jan 28, 2008, at 1:47 AM, grass-user-request at lists.osgeo.org wrote:

> Date: Sun, 27 Jan 2008 19:35:38 +0200
> From: David Epstein <davideps at umich.edu>
> Subject: [GRASS-user] aggregate a field across features and then
> 	display	related charts and histograms
> To: grass-user at lists.osgeo.org
> Message-ID: <1201455338.5659.36.camel at davideps-T43>
> Content-Type: text/plain
>
> Hello,
>
>
> I have looked over a lot of documentation but am still having trouble
> with this task. I hope somebody on the list can point me in the right
> direction!
>
> I have a table of land parcels as polygon features in a postGIS
> database. I have another table of regions in the same postGIS  
> database.
> There are between 20 and 50 parcels to a region. I can access the data
> without a problem (thanks to some helpful people!)
>
> I want to create several maps that aggregate/summarize the parcel data
> and display them as pie-charts and histograms at the centroid of each
> region. For example:
>
> 1. HISTOGRAM of the size of all parcels in the region. The data for  
> this
> is stored in a single field for each parcel. I just need to understand
> how to identify the field, send it to the histogram, and display it at
> the centroid of the region layer.
>
> 2. PIE-CHART where each slice represents the total area owned by a
> particular class of owner. This is more complicated. EACH parcel  
> has an
> area column for each of 7 classes of owners. So, I believe I need to
> keep separate tallies and send them all to a pie-chart function--but I
> am not sure how...
>
> Finally, is the best way to actually KEEP all this data to add new
> columns to the region table with SQL?
>
>
> thank you in advance,
> -david

Sounds like a job for d.vect.chart

Michael
____________________
C. Michael Barton, Professor of Anthropology
Director of Graduate Studies
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

Phone: 480-965-6262
Fax: 480-965-7671
www: <www.public.asu.edu/~cmbarton>