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OpenLayers Cookbook

You're reading from   OpenLayers Cookbook The best method to learn the many ways OpenLayers can be used to render data on maps is to dive straight into these recipes. With a mix of basic and advanced techniques, it's ideal for JavaScript novices and experts alike.

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Product type Paperback
Published in Aug 2012
Publisher Packt
ISBN-13 9781849517843
Length 300 pages
Edition 1st Edition
Languages
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Toc

Table of Contents (15) Chapters Close

OpenLayers Cookbook
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
1. Web Mapping Basics FREE CHAPTER 2. Adding Raster Layers 3. Working with Vector Layers 4. Working with Events 5. Adding Controls 6. Theming 7. Styling Features 8. Beyond the Basics Index

Working with projections


In contrast to other JavaScript mapping libraries, OpenLayers allows working with a great number of projections.

Usually, we specify the desired projection for the map. Later when adding a vector layer to the map, we need to specify to the layer projection so that OpenLayers transforms features from the layer's projection to the map's projection.

But, by default, OpenLayers has a great limitation on projections: we can only use EPSG:4326 and EPSG:900913. Why? Because transforming between projections is not a simple task and there are other great projects that can make it.

So, when we want to work with projections other than EPSG:4326 and EPSG:900913, OpenLayers uses Proj4js Library (http://trac.osgeo.org/proj4js).

Note

Teaching about projections is out of the scope of this book. The EPSG codes are simply a standardized way to classify and identify the great amount of available projections. EPSG:4326 corresponds to the WGS84 (World Geodetic System) and EPSG:900913...

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