Comments on: Assigning Attributes From A Polygon Shapefile To Another Shapefile http://freegeographytools.com/2009/assigning-attributes-from-a-polygon-shapefile-to-another-shapefile Exploring the world of free tools for GIS, GPS, Google Earth, neogeography, and more. Thu, 09 Feb 2012 04:48:22 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Leszek Pawlowicz http://freegeographytools.com/2009/assigning-attributes-from-a-polygon-shapefile-to-another-shapefile/comment-page-1#comment-1399 Leszek Pawlowicz Wed, 15 Apr 2009 16:23:47 +0000 http://freegeographytools.com/?p=3315#comment-1399 If there's a unique identifier for the buildings that gets passed on to the centroids, it should be possible to link the parcel data from the centroid file to building shapefile. If there’s a unique identifier for the buildings that gets passed on to the centroids, it should be possible to link the parcel data from the centroid file to building shapefile.

]]> By: Tyson http://freegeographytools.com/2009/assigning-attributes-from-a-polygon-shapefile-to-another-shapefile/comment-page-1#comment-1400 Tyson Tue, 14 Apr 2009 23:35:11 +0000 http://freegeographytools.com/?p=3315#comment-1400 Regarding the last paragraph: "I could have taken the original building polygon shapefile (used to generate the centroids) as the input shapefile in this process, and the parcel polygon shapefile as the identity shapefile. The result would have been a building polygon shapefile with the appropriate parcel shapefile attributes added to every building’s data in the attribute table." Mostly true. There is a quirk in the MapWindow "Identity of features by Polygon" GIS Tools implementation. Using the building and parcels examples cited in two previous posts, when a building polygon is not wholly located within a parcel polygon (presumably due to errors when converting a raster satellite image to a vector shapefile...) MapWindow will "split" the building into two separate buildings along the parcel boundary. While this may be suitable for some applications, it is not when trying to "assign" parcel data to individual buildings. For this application, it is much better to first find the centroid of each building, then assign the parcel attributes using the centroids. The centroid of each individual building is likely to fall within the boundary of the correct parcel shape, and the resulting shapefile generated by MapWindow will not have "extra" building shapes. Regarding the last paragraph: “I could have taken the original building polygon shapefile (used to generate the centroids) as the input shapefile in this process, and the parcel polygon shapefile as the identity shapefile. The result would have been a building polygon shapefile with the appropriate parcel shapefile attributes added to every building’s data in the attribute table.”

Mostly true. There is a quirk in the MapWindow “Identity of features by Polygon” GIS Tools implementation. Using the building and parcels examples cited in two previous posts, when a building polygon is not wholly located within a parcel polygon (presumably due to errors when converting a raster satellite image to a vector shapefile…) MapWindow will “split” the building into two separate buildings along the parcel boundary. While this may be suitable for some applications, it is not when trying to “assign” parcel data to individual buildings. For this application, it is much better to first find the centroid of each building, then assign the parcel attributes using the centroids. The centroid of each individual building is likely to fall within the boundary of the correct parcel shape, and the resulting shapefile generated by MapWindow will not have “extra” building shapes.

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