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<!DOCTYPE html>
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<title>map school: Topology: a free introduction to geo</title>
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<h1><a href='./'>map school: Topology</a></h1>
<p>a free introduction to geo.</p>
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<p>In addition to storing places and shapes, some vector data keeps track of topology, the relationships between different shapes that touch. For instance, political borders often touch - you can stand with one foot in Arizona and another in New Mexico. A lot of geospatial data, though, will have one shape that represents Arizona and another that represents New Mexico, with two borders that precisely overlap, but have no other association.</p>
<p>This gets tricky when you want to do something like ask 'which states touch?' or simplify the shapes of objects while preserving borders lined up. We use the concept of topology: some vector data, instead of storing a shape of Arizona and another of New Mexico, saves a bunch of lines and keeps track of which ones form the boundary of which object. So, the border between Arizona and New Mexico is a single line that's used to draw the border of both states, and if you modify the line, it changes the shape of both states.</p>
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