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 unique value rules


Usually, we do not only style features by what they represent, for example a city or a village, but we style depending on their attributes, such as the number of citizens, year of foundation, and number of squares.

To help on these cases, OpenLayers offers us the possibility to define rules to decide how to style features. For example, we can define a rule that for all features of a city with a population greater than 100,000 a point with radius 20 and color brown can be rendered, while for cities with a population less than 100,000, a point with radius 10, color orange, and semi transparent can be rendered.

Beginning in the world of the rules, the concept of unique value rules are the simplest case we can find. The idea is simple, apply one style or another depending on the value of a feature's attribute.

In this recipe, we are going to load a GeoJSON file, with some cities of the world, and apply a rule that will set the radius of the points depending on the...