WebGIS application with OpenLayers 2 - Part 1: Layer tree

Creating a whole WebGIS application is a time-consuming task, which can be eased with toolkits, like GeoExt or Heron MC. However, using such a toolkit, has some disadvantages. For example, you can't keep step with the evolution of the mapping libraries, as the toolkits can't develop so rapidly. If you want to use the most recent features, and don't want to wait for the developers of your favourite toolkit to come up with a new version, you have to build your application just on the library.
From another point of view, learning how a web mapping library works can be rewarding. If you build your WebGIS application, you can easily come across a situation, where you have to customize it in a way, that hasn't been implemented in your toolkit. At this point, you will need to learn how to use the native library anyway (and consider yourself lucky, if you don't work with a deadline). To avoid such a case, it is considerable to get acquainted with the library in time and use toolkits later. In the next few posts, I will demonstrate how to build a basic WebGIS application with only HTML, JavaScript, and OpenLayers 2. I will try to summarize the content of the last few posts, and show how to handle browser events with the library.

OpenLayers layer management

In the previous post I wrote about layer creation. This is only a part of the capabilities of a good GIS application. A good application can also manage layers in an efficient way. Fortunately, OpenLayers libraries have predefined functions for layer management. They provide a great base to build upon and create dynamic Web GIS applications. Some of the basic tasks of layer management are adding and removing layers, changing layer order, listing rendered layers, and changing layer styles. Off course, they have to do it during the workflow, without reloading the page. I will show a few of these functions with a live example in this post.

OpenLayers layer creation

Layers are a core concept in every GIS software. They are collections of contiguous spatial data. You can stack layers on each other, perform an operation on them, style them individually, etc. Fortunately, OpenLayers is outstanding with its layer management. Every raster dataset is contained in a layer. For vector data, you can group features to as many layers as you like. Layers can be accessed, modified or removed after they are constructed. As the layer changes, the map object will track the changes, so it will take effect on the visualization, too. In the following post, I will write about OpenLayers layers.