Hi Peter,
One way to do your query would be using the following SQL example:
I'm assuming the following naming conventions (so just replace them for your
situation):
A Management Unit and a Land Use Table called Manage and Land with a column
in each called Name (ie the description of the management unit and land use)
Select Manage.Name, Land.Name, Sum(ProportionOverLap(Manage.obj,Land.obj)*100)
from Manage, Land where Manage.Obj Intersects Land.Obj Group by Manage.Name,
Land.Name
Browse * From Selection
As a check you could run the following query to see if they tally up to 100
percent (ie that's if your land use polygons overlay the management units totally).
Select Manage.Name, Sum(COL3) From Selection Group By Manage.Name Into CHECK
Browse * From CHECK
The ProportionOverlap command returns the percent of overlap one object covers
another which in this case would be better than using just the AreaOverlap command.
Hope this helps.
Regards,
Sue.
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>I have a tricky SQL someone might be able to help me with (at least, it's
>tricky for me).
>I have two tables of polygons, one is land use, the other are management
>units. I need a breakdown of land use within each management unit. I need to
>be able to say for example, "management unit Type A comprises 10% cropping,
>and 90% grazing land use."
>
>There was a discussion not long ago about the use of the AreaOverlap
>function, but I can't seem to make it work for me. It would be nice if I
>could do this by calculating proportion overlap, rather than having to split
>the land use polygons. The two files are very big and complex.
>
>Any ideas?
>
>
>Regards
>
>Peter Walsh
>Dames & Moore
>email: [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
>Ph. +61 (2) 9955 7772
>
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