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#1
cmdrico7812

cmdrico7812

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I
have a shapefile of zip codes in Michigan that has the number of
non-profit organizations in each zip code in the data. I also have a
shapefile of the legislative districts in Michigan. I want to be able
to map the number of organizations in each legislative district. The
problem is that legislative districts don't conform to any type of
governmental boundary so some districts overlap 3 or more zip code
areas. Does anyone know of a way that I can accurately transfer the
information pertaining to each zip code to the legislative districts?
I've tried Spatial Joining but it doesn't work because districts
overlap zip code boundaries. Thanks in advance.

Eric

#2
Martin Gamache

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"


have a shapefile of zip codes in Michigan that has the number of 
non-profit organizations in each zip code in the data.  I also 
have a shapefile of the legislative districts in Michigan.  I want 
to be able to map the number of organizations in each legislative 
district.  The problem is that legislative districts don't conform 
to any type of governmental boundary so some districts overlap 3 or 
more zip code areas.  Does anyone know of a way that I can 
accurately transfer the information pertaining to each zip code to the 
legislative districts?  I've tried Spatial Joining but it doesn't 
work because  districts overlap zip code boundaries.  Thanks 
in advance.

Eric

http://



There are a couple of ways to do this.

However
one of the problems with your question is how do you want to partition
the data. Since you have a many to many relationship are you prepared
to have zip code regions be allocated to more than one legislative
district or only to one. Then the question becomes to which one? Since
you dont know where the Non-Profits are located you make some
assumptions about the distribution and that may be problematic.

I
can envision a scenario in which you convert one of your polygon
datasets to a point dataset using either the geometric centroid or the
center of gravity and you then do a spatial link using the polygon that
contains the centroid. That gives you a one to one.

Another
option is to clip one dataset with another and end up with small
polygons that contain all the attributes of the original and then do
the spatial join, this allows you to pass on all the attributes of
every polygon that intersects with the other. This means your Non
Profits will get counted more than once...i.e. in more than one state.

I
dont really see an elegant solution to your problem since your admin
units dont match your zip code boundaries very well. Best to try and
track down the original NP dataset and recalculate the densities based
on your legislative districts. If you can't do that then make sure you
have a nice disclaimer on your map explaining these are estimates... "

#3
cmdrico7812

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I
used the create zip code centroid method you gave and it worked exactly
like I wanted it to. I feel it gives the best representation based on
the information that I have. Thanks a ton!




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