[GRASS-user] Extracting an area with maximum value

[Michael Barton]

This is a database query issue. You need something along the line of
[newfield] = max([oldfield1],[oldfield2],...)

I don't know the exact syntax in SQL, but maybe this can point you in the
right direction.

Michael


On 11/20/07 4:58 PM, "Corey Moffet" <cmoffet at pw.ars.usda.gov> wrote:

> Dear GRASS users,
> 
> I have a vector layer with area features that have 1 or more categories
> and associated attributes linked with the centroid.  I would like to
> extract a single category for each centroid on the basis of some
> attribute.
> 
> For example, there are several areas in my study area and each area has
> a fire history. The area may have been burned in one or more years.  In
> one area, lets say it burned in 1950 and 1970 so the centroid for this
> area has 2 categories linked with it and the attribute YearBurn is 1950
> and 1970 for the 2 categories, respectively.  I want a new layer that
> has only one category linked to the centroid and the value 1970 (e.g.,
> max(YearBurn) as LastBurn) for the attribute "LastBurn."
> 
> The database table is in dbf format.  How can this be accomplished
> without having to edit it by hand?

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

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton