Book Image

OpenLayers Cookbook

Book Image

OpenLayers Cookbook

Overview of this book

Data visualization and analysis has become an important task for many companies. Understanding the basic concepts of GIS and knowing how to visualize data on a map is a required ability for many professionals today. OpenLayers is a JavaScript library to load, display, and render maps from multiple sources on web pages."OpenLayers Cookbook" teaches how to work with OpenLayers, one of the most important and complete open source JavaScript libraries.Through an extensive set of recipes, this book shows how to work with the main concepts required to build a GIS web applicationñ maps, raster and vector layers, styling, theming, and so on."OpenLayers Cookbook" includes problem solving and how-to recipes for the most common and important tasks. A wide range of topics are covered.The range of recipes includes: creating basic maps, working with raster and vector layers, understanding events and working with main controls, reading features from different data sources, styling features, and understanding the underlying architecture."OpenLayers Cookbook" describes solutions and optimizations to problems commonly found.
Table of Contents (15 chapters)
OpenLayers Cookbook
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
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...