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Posted by YL on February 21, 2004, 8:07 pm
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>
> >Does anybody know how i can generate 1-mile grid that is present
> >on us maps in State Plane Coordinate System.
> >I need one for zone 5 (Alaska).
> >Where its starting point and why rows of the grid cells sometimes shift?
> >whithin the same map.
> >
> >Thanks!
> >
> >
>
>
> This sounds very much like the "township and range" grid system widely
> used in the USA. As it is a survey based system, you can't simply
> generate it accurately - you need to get the data from somewhere.
> Others will no doubt suggest where!
>
> Basically much of the USA was surveyed into east-west bands, and each
> range then subdivided into square parcels. Because of the convergence
> of the meridians, the north-south boundaries don't match across
> latitude lines, so you get the shifts you mention. Theoretically ypu
> could, by knowing the origins of the grid, calculate the offsets. In
> practice, the grid is actually marked on the ground with survey
> stakes, and relatively minor erors in the survey mean that it is the
> position of those stakes that is definitive. E&OE - you need an
> American surveyor (which I am not) to give the full details.
>
> Paul
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