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From |
"David Torres" <writeon4truth2@msn.com> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
Re: st: Nearest distance (spatial) and shp2dta question |

Date |
Thu, 2 Jul 2009 14:59:10 -0400 |

Mr. Nichols, I am thinking about your point regarding getting average distances from postsecondary institutions to potential students. I may add this approach to what I'm doing, so any advice you can give on this and my current main approach is greatly appreciated. Learning Stata is fun, indeed. DT ----- Original Message ----- From: "Austin Nichols" <austinnichols@gmail.com> To: <statalist@hsphsun2.harvard.edu> Sent: Thursday, July 02, 2009 11:50 AM Subject: Re: st: Nearest distance (spatial) and shp2dta question > David Torres<torresd@umich.edu>: > Each of (1) and (2) is easy to do (if time-consuming) with a single > loop over observations. > > Note that the main trick in my code was to do > a nonmatched -merge- to get both datasets in memory at once. You will > have to be a bit more clear about what you want to get more specific > advice: "calculate distances between census tract and county centroids > to the nearest [school] with population of the tracts or counties used > as weights" sounds like you want the final dataset to have one obs for > each institution with some kind of average distance to potential > students, but (2) says you want one obs per centroid. What are these > calculations to be used for? Maybe that answer will help clarify what > you need. > > On (3), what data do you have? Polygon vertices? How big are the > polygons (i.e. is the curvature of the Earth important)? Is this for > calculating centroids for use in (1) and (2)? > > On Thu, Jul 2, 2009 at 10:42 AM, David Torres<torresd@umich.edu> wrote: > > Three comments/questions: > > > > 1. I was just browsing the web looking for something similar to Cox's > > nearest .ado file and stumbled on the example Austin Nichols gave for > > calculating distances between two different sets of xy coordinates, > > originally from two different data sets. I am not familiar with the code > > he > > gave so I have to ask: Is there an .ado file that can do all that work > > for > > me? I mean, if I already have two data sets that I've merged, is there a > > simple command I can input that will give me additional distance > > variables > > to work with? > > > > What I'm trying to do is calculate distances between census tract and > > county > > centroids (for the entire US, AK, and HI) to the nearest postsecondary > > institution (of all types and by sector and control of institution: > > public, > > private, proprietary, pub2year, priv2year, prop2year, pub4year, > > priv4year, > > prop4year), with population of the tracts or counties used as weights. > > > > 2. I also would like to produce variables for the total number of > > institutions that fall within a 10, 20, 30, 40, 50, and 100 mile radius > > of > > each tract and county centroid. > > > > I can do all of this in ArcGIS, to be sure, but with eight years of > > data, > > and ten different .dbf/.shp files per year, this would be a tedious > > chore. > > I would prefer to spend an hour and write a .do file that will do in > > minutes what it will take hours to do in ArcMap/ArcInfo. > > > > 3. The shp2dta command produces xy coordinates for area centroids that I > > am > > not familiar with. Does anyone know if the code in the .ado file can be > > changed to produce what I want--regular xy or lat/lon coordinates? > > > > With regard to the first two parts of my questions, here is Austin > > Nichols' > > code, the first part of which I don't really care about: > <snip> Any help anyone can offer is greatly appreciated. > > > > Thanks, > > > > David Torres > > * > * 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/ > * * 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: Nearest distance (spatial) and shp2dta question***From:*David Torres <torresd@umich.edu>

**Re: st: Nearest distance (spatial) and shp2dta question***From:*Austin Nichols <austinnichols@gmail.com>

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