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Hey all, I'm somewhat of a newb when it comes to creating mapping solutions. I've stayed on a pretty high level playing with openlayers and pulling data from various webservices.

The first part of my question is the realm of how do I compute polys?

I understand poly basics, such that it's a 2 dimensional shape that you can create a boundary with. For example, when you enter your zip code in the following example. The red line illustrates the boundaries, which is understood as a poly, correct? Could you link me information on this concept, and how to create polygons and how to work with them. I'm very fluent in python, and I think there is a GIS-python module/postgre-gis?

The second part is, how do I go about matching coordinates in said polys? What is the algorithm I need to make this happen? Is there an open-source project that I can use to calculate this? Preferably in c++ or python.

Third, where can I obtain datasets of Country, State/Territory, County/Providence, City/Town, Neighborhood.

Thanks in advance!

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    More than One Question in there - For Openlayers? Google Maps? - Which area for datasets are you interested in? data quality varies across the globe. – Mapperz Mar 17 '11 at 16:44
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Openlayers GML (Polygon construction)

        <ms:msGeometry>
16          <gml:MultiPolygon srsName="EPSG:4326">
17          <gml:polygonMember>
18            <gml:Polygon>
19              <gml:outerBoundaryIs>
20                <gml:LinearRing>
21                  <gml:coordinates>-0.318987,47.003018 -0.768746,47.358268 -0.574463,47.684285 -0.347374,47.854602 -0.006740,47.925567 0.135191,47.726864 0.149384,47.599127 0.419052,47.670092 0.532597,47.428810 0.305508,47.443003 0.475824,47.144948 0.064225,47.201721 -0.318987,47.003018 </gml:coordinates>
22                </gml:LinearRing>
23              </gml:outerBoundaryIs>
24              <gml:innerBoundaryIs>
25                <gml:LinearRing>
26                  <gml:coordinates>-0.035126,47.485582 -0.035126,47.485582 -0.049319,47.641706 -0.233829,47.655899 -0.375760,47.457196 -0.276408,47.286879 -0.035126,47.485582 </gml:coordinates>
27                </gml:LinearRing>
28              </gml:innerBoundaryIs>
29            </gml:Polygon>
30          </gml:polygonMember>
31          </gml:MultiPolygon>
32          </ms:msGeometry>

http://trac.osgeo.org/openlayers/browser/trunk/openlayers/examples/gml/polygon.xml

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  • This only answers the first part of the question. – jbcurtin Mar 17 '11 at 17:02
  • Yes it does, depends on your data source - you need to have a geoprocessing database (postgis) to INTERSECT the Polygon and select the points – Mapperz Mar 17 '11 at 18:08
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Natural Earth (http://www.naturalearthdata.com/) will provide you with global countries and first order admin areas (states etc).

In the USA the Census bureau is the best place to find boundaries http://www.census.gov/geo/www/tiger/ will get you counties and townships etc. In other countries that data may or may not be freely available.

Neighbourhoods are trickier as they tend to be a bottom up concept not a top down boundary, try the Flickr shapefiles (http://flowingdata.com/2008/11/28/neighborhood-boundaries-with-flickr-shapefiles/).

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For your other question see https://secure.wikimedia.org/wikipedia/en/wiki/Point_in_polygon for a description of how to determine if a point is in a polygon.

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You can download neighborhood data in shapefile from Zillow (quote from their website):

The Zillow data team has created a database of nearly 7,000 neighborhood boundaries in the largest cities in the U.S. And we'd like to share them with you! We're sharing these neighborhoods under a Creative Commons license to allow people to use and contribute to our growing database.

http://www.zillow.com/howto/api/neighborhood-boundaries.htm

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