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How to display a map using Polymaps JS library
Most mapping libraries focus on 256×256-pixel image tiles, with only limited support for dynamic overlays such as county boundaries and point clouds. These libraries assume that data needed to produce the desired overlay can be loaded into memory all-at-once, making it difficult to visualize large datasets. Furthermore, while image tiles automatically adjust in resolution as the map zooms in or out, the overlay resolution remains constant; this greatly limits multi-scale exploration of data, as the resolution must be fixed either for macro- (e.g., state-level) or micro- (e.g., block-level) observation.
The goal of Polymaps is to better support rich, large-scale data overlays on interactive maps by extending the tile metaphor to vector graphics: in addition to standard image tiles, Polymaps supports vector tiles that are rendered with SVG. The vector geometry is loaded as GeoJSON via asynchronous XMLHttpRequest; Point geometry objects are rendered as SVG circle elements, Polygons as paths, and so on. By loading geometry at known tile boundaries, requests can be issued efficiently on-demand by the client, and responses trivially cached on the server. When the user zooms in, geometry can be seamlessly refined to show greater detail, while on zoom out, geometry can be simplified to improve performance.
- Full documentation for this library is at the Polymaps.org main site.
- A phone device supporting with Web Runtime support installed.
- You can use a code editor of your choice, but this example is build with Aptana Studio and the WRT S60 plugin.
Note: Aptana has been superseded by the Nokia Web Tools, an IDE and Simulator based on Aptana and Eclipse.
For this example we will create a default WRT S60 widget, with the following files
index.html basic.css basic.js
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
<title> Sample web app</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<link rel="stylesheet" href="basic.css" type="text/css" />
<meta name="Generator" content="Nokia WDE 3.0.0" />
//The stylesheet is not implemented for this example.
var po = org.polymaps;
var map = po.map()
+ "/1a1b06b230af4efdbb989ea99e9841af" // http://cloudmade.com/register
.hosts(["a.", "b.", "c.", ""])));