Web mapping is the second major component of this project. The Wikipedia description of “web mapping” is:
Web mapping is the process of designing, implementing, generating and delivering maps on the World Wide Web and its product. ...
Ian Turton, in his lecture notes for Penn State's Geog 585 (op. cit.) class, defines “web mapping” thus:
Generally, when we talk about web mapping we mean a map that you can interact with, zoom in and out, pan around, change what you are looking at, etc.
Turton's definition is the appropriate one for our open source project. Web maps are yet another, highly effective, means for disseminating the data and information compiled and created by the townships' GIS activities.
Initially, the project will start with two types of web maps. The first type uses the standards-based web mapping services established by the Open Geospatial Consortium (OGC). This type of map uses base maps and data layers served from map servers that comply with the standards established by OGC.
Again, quoting Ian Turton from his lecture notes from Geog 585 and Geog 583, of the twenty or so OGC standards, the ones most commonly encountered in web mapping are as follows:
These standards are used in one aspect or other of web mapping. WMS, WFS, and WCS are concerned with the serving of various types of data (map images and feature attributes) over the web. GML, Simple Feature, and KML are concerned with describing the geometries of various geographic features (as well as styling them), while SLD concerns itself almost exclusively with styling a geographical feature. The KML standard, which can also carry feature attribute data, originated in Google Earth and Google Maps, and eventually was adopted by the OGC.
The “thin clients” that request, receive, and render these map images from such servers onto web browsers also tend to be open source software packages. Open Layers is one of the best known “thin clients.” Newer ones include rendering packages like Mapnik. Standards-compliant map server packages such as GeoServer and MapServer are also open source. We will call web mapping applications created using such open source tools Open Web Mapping.
Michelle Ballinger (MGIS, Penn State 2011) has laid out a basic framework for open web mapping at her capstone project website. In this framework, she advocates the use of open source GIS software to produce and style the basic web map layers. The styling for each of the data layers is then converted to a form (SLD files) usable by the open source map server of choice, GeoServer. The website continues with instructions on setting up the thin client (OpenLayers) and the map server, and loading the web map onto a web site. This model forms one of this project's two open web mapping procedures. Another option uses a basic web server directly without using GeoServer to serve data layers. (See the Open Web Maps section that follows.)
Another type of web maps uses proprietary map servers and copyrighted base map tiles. The owners of such servers and map tiles publish application programming interfaces (API's) that allow the public free access to these map services. Examples of such proprietary services that allow free access include Google Maps, Bing Maps, and Yahoo! Maps. To differentiate this type of web mapping from open web mapping, we will call maps created thus Mashups, as in Google Mashup or Bing Mashup. Thus far, project participants have preferred Google Mashups over the other services, probably due to greater familiarity with Google Maps.
The third type of web mapping is a new technology that is a subset of Open Web Mapping, specific to the open source desktop software QGIS. Known as QGIS Server, it is now distributed with all versions of QGIS. Initially developed for Linux versions of QGIS, this system uses the QGIS rendering engine to convert a QGIS project to a map image that is served from a WMS server established from within Apache web server. As of this writing, this project has not yet implemented any QGIS Server-based web maps, but expect to do so within a few months. Because project participants can use their QGIS project files directly to create web maps, this technology holds great promise.
Each of these web mapping systems will be discussed in more detail in the following sub-sections.
The Project >