William Hindman
wdhindman at dejpolsystems.com
Sat May 5 08:05:03 CDT 2007
...good link Stu ...I can put that to immediate use with a current client ...thanks. William Hindman ----- Original Message ----- From: "Stuart McLachlan" <stuart at lexacorp.com.pg> To: "Access Developers discussion and problem solving" <accessd at databaseadvisors.com> Sent: Saturday, May 05, 2007 7:46 AM Subject: Re: [AccessD] code to find the population within a radius of azipcode >A nice tool if you want to build your own database of lat/long of > towns/cities is Geomaker: > GeoMaker - Create the GeoDatabase for the entire world. This program > create > the geographical location Latitude, Longitude, and Altitude (Elevation) > for > every city, village, region, state, county in the World. The program > crawls > the data from the website www.heavens-above.com which collect data from US > Geological Survey for the USA (and dependencies) and The National Imaging > and Mapping Agency for all other countries. The program is available as > .exe and the source code in Visual Basic 6 > > http://geomaker.mewsoft.qarchive.org/ > > Note that it takes a looong time to grab all the locations in a country > :-( > > It grabbed 22,000 records for PNG. After I dumped them into an Acess table > and de-duped the names, I ended up with over 9000 locations - many of > them > small villages/hamlets including 27 localities/suburbs within the National > Capital District. > > > On 5 May 2007 at 6:54, William Hindman wrote: > >> ...when you are using zip based lat-longs to calculate radius, the >> concept >> of "accuracy" is about as relevant as nasal drip regardless of which >> algorithms you use ...a zip based lat-long is the geo center of the zip >> code's mapped area ...since zip areas are highly irregular the given geo >> center may well be physically outside the zip's actual boundaries ...and >> then there is the problem of zip area geographical size which is most >> often >> based upon demographics ...ergo, the size of an Alaskan zip code can be >> several hundred miles in extent while that of a Manhattan zip may be >> resolved to a few floors in a single office tower ...thus search results >> for >> zips within a fifty mile radius of a given zip's lat-long should be >> considered with the same levity reserved for JC's stick poking efforts >> ...the calculation of the number of bubbles per poke being about as >> accurate. >> >> William Hindman >> >> ----- Original Message ----- >> From: "MartyConnelly" <martyconnelly at shaw.ca> >> To: "Access Developers discussion and problem solving" >> <accessd at databaseadvisors.com> >> Sent: Friday, May 04, 2007 4:35 PM >> Subject: Re: [AccessD] code to find the population within a radius of a >> zipcode >> >> >> >I would like to see code too. There are many possible errors. >> > >> > How accurate do you want to be. Third order surveying accuarcy? >> > Generally >> > lat/long with 3 decimal places accuracy gives you 100 metre error >> > lat/long with 4 decimal places gives 10 metre error >> > >> > Other errors. >> > >> > The shape of the Earth more closely resembles a flattened spheroid >> > with extreme values for the radius of curvature, or arcradius, of >> > 6335.437 km >> > at the equator (vertically) and 6399.592 km at the poles >> > and having an average great-circle radius of 6372.795 km (3438.461 >> > nautical miles). >> > >> > Using a sphere with a radius of 6372.795 km thus results in >> > a probable error of up to about 0.5%. >> > >> > Examples: >> > >> > This is a circle on the surface of the planet. At larger radii, >> > the effects of the Mercator projection become clearly visible. >> > Try a 2000 mile radius and move mouse to see if point within a circle >> > or >> > is it an egg? >> > >> > http://maps.forum.nu/gm_sensitive_circle2.html >> > >> > This circle is actually tangent to the surface of the Earth, >> > but for small radii this is of little significance. >> > >> > http://maps.forum.nu/gm_clickable_circle.html >> > >> > >> > >> > Borge Hansen wrote: >> > >> >>>John Colby wrote: >> >>>I converted the code to find the population within a radius of a zip >> >>>code. >> >>> >> >>> >> >> >> >>Hi John, >> >>What does your VBA code look like? >> >> >> >>I am using a code that will find a subset of records based on their >> >>geocode within a near enough square, >> >> >> >>...and querying the recordset like this >> >> >> >>....find me all record instances where Lat of record is between >> >>"northernmost Lat" and "southernmost Lat" and Long of record is >> >>between "most western Long" and "most eastern Long" >> >> >> >>Interested to see your code based on a circle construct..... >> >> >> >>Regards >> >>borge >> >> >> >> >> >> >> > >> > -- >> > Marty Connelly >> > Victoria, B.C. >> > Canada >> > >> > -- >> > AccessD mailing list >> > AccessD at databaseadvisors.com >> > http://databaseadvisors.com/mailman/listinfo/accessd >> > Website: http://www.databaseadvisors.com >> > >> >> >> >> -- >> AccessD mailing list >> AccessD at databaseadvisors.com >> http://databaseadvisors.com/mailman/listinfo/accessd >> Website: http://www.databaseadvisors.com > > -- > Stuart > > > -- > AccessD mailing list > AccessD at databaseadvisors.com > http://databaseadvisors.com/mailman/listinfo/accessd > Website: http://www.databaseadvisors.com >