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From |
"Sergio I Prada" <sprada1@umbc.edu> |

To |
statalist@hsphsun2.harvard.edu |

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

Date |
Fri, 3 Jul 2009 09:40:06 -0400 (EDT) |

Here another resource (which I got before from the kind people at Stata): Havershine is a user written command that calculates the distance using the Haversine formula, Vincenty formula, and/or the Law-of-Cosines-based formula. Type the following to install this command: net describe vincenty, from(http://fmwww.bc.edu/RePEc/bocode/v) net install vincenty Then, type -help vincenty- to view the help file. By using the hav() option you can calculate the distance using the Haversine formula instead of manually entering the equation. Also, the default is to express the distances in miles but you can change this to kilometers with the in km option. See one example here ********************* use testdistance, clear set more off sort patient gen id = _n qui levelsof patient, local(patients) qui gen shortest_dist = . qui gen matched_hos = . foreach p of local patients { preserve qui keep if patient==`p' local pat_long = pat_long[1] local pat_lat = pat_lat[1] local obs = id[1] restore vincenty `pat_lat' `pat_long' hos_lat hos_long, hav(h) replace summarize h qui replace shortest_dist = `r(min)' in `obs' preserve keep if round(h,.00001) == round(`r(min)', .00001) local id = hospital[1] restore qui replace matched_hos = `id' in `obs' } drop id *********************** This is calculating the straight distance from the patient to the hospital. This is not taking into consideratin any physical land barriers, such as mountains and rivers. -- Sergio I. Prada, PhD (Candidate) Department of Public Policy University of Maryland, Baltimore County 1000 Hilltop Circle, Baltimore, MD 21250 Phone: 410-455-6527 * * 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/

**Follow-Ups**:**st: Re: Nearest distance (spatial) and shp2dta question***From:*"David Torres" <writeon4truth2@msn.com>

**st: Re: Nearest distance (spatial) and shp2dta question***From:*"David Torres" <writeon4truth2@msn.com>

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