Map Projections

When displaying geospatial data you’ve got some decisions to make about what map projection to use.  One way to look at it is this: the world isn’t flat.  I know that isn’t news in the 21’st century, but that does turn out to be the problem.  The world isn’t flat, but the map is.  There…

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Transforming Map Data for Display

Now that we’ve got some map data it would be great to actually display it.  But that still isn’t an easy job.  The problem is that we’ve got two wildly different coordinate systems.  For the map data, we’ve got degrees latitude and degrees longitude and for our display surface we’ve got window coordinates with the…

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Getting geospatial data from shapefiles #2

In my last post we were able to read the header.  This time, we’ll actually drill in and get some actual map data.  To start reading the individual records in the file we’ll need some more data structures. All of the shape records in the spec appear to have this form:       // Copyright…

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Getting geospatial data from shapefiles

There are lots of digital map files available from the Government.  And in the case of the national atlas the data is stored in shape files.  And, as luck with have it, shape files are easy to read. The ESRI Shapefile Technical Description is easy to find and download.   The shapefile I’m using is statesp020.tar.gz. …

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Blogging Again

It’s been more than 5 years since I wrote something in my blog. But it is about time to get back to it.  One of the things I’ve been playing with off and on in my spare time is location data.  This has been a long time interest.  As a matter of fact before I…

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