August 2018
Intermediate to advanced
272 pages
5h 3m
English
Content preview from JavaScript and Open Data
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13Cartographic Data
13.1. Cartographic application: using cartographic libraries
A cartographic application is of a level of complexity greater than a simple graphic plot, as we have described earlier. We will not try to code it ourselves, even if, for most of the libraries (open source or proprietary), they just draw on a <canvas>. There are various methods for drawing lines or polygons or pixel matrices, for computing topological relations such as sharing a vertex, being included or intersecting each other, and also for computing distances, transforming geographical coordinates between map projections, etc.
It is not our intention to detail any of these numerous features. We will merely present the basic use of one library, open source, which is complete enough to sample all of the most useful features, in a way similar to those of proprietary libraries such as Google, Bing and Yahoo. That library is OpenLayers, code licensed under the “2-Clause BSD”, with a very active community (2006–2017): at the time of writing this book, the latest version is v4.6.5 (March 18, 2018).
The requirements are the library, the basic styles, and a simple <div> element (or a <canvas>) that will be used by the library:
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/openlayers/4.6.4/ol.css"><body><div id="olmap" class="olmap"></div><script src="https://cdnjs.cloudflare.com/ajax/libs/openlayers/4.6.4/ol.js"></script>
In this application, we use data from four ...
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