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From |
"Dimitriy V. Masterov" <dvmaster@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Computing minimum driving distance to an area (rather than a specific point) |

Date |
Mon, 16 Apr 2012 10:30:54 -0400 |

I just realized that I left out the part about how you would read in the shapefiles into Stata. You need a command from ssc called shp2dta (or mif2dta if you have MapInfo format boundaries). DVM On Mon, Apr 16, 2012 at 9:46 AM, Dimitriy V. Masterov <dvmaster@gmail.com> wrote: > Jen, > > In a geometric sense, you can think of your municipalities as > polygons. Every polygon has at least 4 distinct barycenters (i.e., > centers of mass), so there's no straightforward answer to your > question. > > 1) The barycenter of its vertices. > 2) The barycenter of its edges. > 3) Its barycenter as a polygon, which can be obtained decomposing it > into triangles. The area-weighted average of these barycenters is the > polygon's barycenter. > 4) X-weighted centroid, where X might be a people or blocks or block groups. > > These may coincide in special cases, but are generally distinct > points. It may also happen that many of these centers are not > necessarily located within the interior of a polygon. Hopefully your > municipalities will be mostly convex, so this should be less of a > problem. You do have to worry that your barrycenter is in the middle > of lake, for example. > > The three types differ on where the mass is presumed located: it > either is entirely on the vertices, spread uniformly on the edges, or > spread throughout the polygon itself, either uniformly or not. > > You might be able to hack such calculations in Stata using the > coordinates file that you create when you convert the shapefile for > the municipal boundaries, but I think there's an easier way. I would > get the shapefile for the municipalities. Such files will usually have > columns for the lat and lon of the centroid. It's what ArcGIS uses > when you choose to label an area. Use that as your center. > Alternatively, you might want to see if you can track down a > population-weighted centroid as that seems relevant to your problem. > From then, it will just be a simple merge. > > HTH, > DVM * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: Computing minimum driving distance to an area (rather than a specific point)***From:*Jen Zhen <jenzhen99@gmail.com>

**Re: st: Computing minimum driving distance to an area (rather than a specific point)***From:*"Dimitriy V. Masterov" <dvmaster@gmail.com>

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