[GRASS-user] Extracting an area with maximum value

GRASS GRASS user
1

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?

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With best wishes and kind regards I am

Sincerely,

Corey A. Moffet
Rangeland Scientist

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2

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@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