forked from OSGeo-ES/mapschool
-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathsection-topology.html
59 lines (57 loc) · 3.7 KB
/
section-topology.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
<!DOCTYPE html>
<html>
<head>
<meta charset='utf-8'>
<title>mapschool: Topology: a free introduction to geo</title>
<link rel='stylesheet' type='text/css' href='css/site.css' />
<meta http-equiv='content-type' content='text/html; charset=utf-8' />
<meta name='viewport' content='initial-scale=1.0 maximum-scale=1.0'>
<meta name='description' content='a brief introduction to map and geospatial concepts'>
<link rel='shortcut icon' href='img/library-24.png'>
</head>
<body>
<div class='header'>
<h1><a href='./'>mapschool: Topology</a></h1>
<p>a free introduction to geo.</p>
<nav>
<a href='./'>home</a>
<a href='https://github.com/tmcw/mapschool'>code</a>
<a href='https://tmcw.wufoo.com/forms/mapschool-feedback/'>feedback</a>
<a href='https://raw.github.com/tmcw/mapschool/gh-pages/mapschool.epub'>ebook</a>
<a href='./furtherreading.html'>further reading</a>
</nav>
</div>
<div class='wrap'>
<div class='content'>
<p>In addition to storing places and shapes, some vector data keeps track of topology, the relationships between different shapes. 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>
<div id='disqus_thread'></div>
<script type='text/javascript'>
/* * * CONFIGURATION VARIABLES: EDIT BEFORE PASTING INTO YOUR WEBPAGE * * */
var disqus_shortname = 'mapschool'; // required: replace example with your forum shortname
/* * * DON'T EDIT BELOW THIS LINE * * */
(function() {
var dsq = document.createElement('script'); dsq.type = 'text/javascript'; dsq.async = true;
dsq.src = '//' + disqus_shortname + '.disqus.com/embed.js';
(document.getElementsByTagName('head')[0] || document.getElementsByTagName('body')[0]).appendChild(dsq);
})();
</script>
<noscript>Please enable JavaScript to view the <a href="http://disqus.com/?ref_noscript">comments powered by Disqus.</a></noscript>
<a href="http://disqus.com" class="dsq-brlink">comments powered by <span class="logo-disqus">Disqus</span></a>
</div>
</div>
<script type='text/javascript'>
var _gauges = _gauges || [];
(function() {
var t = document.createElement('script');
t.type = 'text/javascript';
t.async = true;
t.id = 'gauges-tracker';
t.setAttribute('data-site-id', '528a6fcff5a1f56dc400009f');
t.src = '//secure.gaug.es/track.js';
var s = document.getElementsByTagName('script')[0];
s.parentNode.insertBefore(t, s);
})();
</script>
</body>
</html>