Using Open Web Services

C. WFS - Abstract Access to your Data

WFS - Abstract Access to your Data

The Web Feature Service (WFS) is easily one of the most valuable specifications of the OGC. It provides a generic way to access raw geographic data over the web. To the general user, this can potentially provide a wealth of information embedded in the map being viewed. The WMS specification has an operation built in to give this functionality - GetFeatureInfo (link), but it remains a bit hacky - the main problem is that the area of selection can only be a point, and on many servers it can be hard to hit the exact pixel needed to get information. But using a WFS gives much more control over how to actually access that data. Complex Filters (link) serve as the OWS equivalent of a SQL WHERE statement, allowing you to select all four lane roads that are longer than 2 kilometers that start with D, for example.

The other feature of interest to users is 'Transactions', being able to insert, update, and delete feature on a map. The GeoServer User's map (link) is an example of this, where users can zoom and select 'Add User' on a certain point, and it will be inserted into the backend database. Locking allows additional control over transactions, so that users do not overwrite data others are modifying.

In short, WFS leads to greater transparency and openness in mapping applications. Instead of merely being able to look at a picture of the map, as the provider wants the user to see, the power is in the hands of the user to determine how to visualize the raw geographic and associated data. The data can be downloaded and given further analysis and combined with other data, or it can be chained with other web services to do even more interesting things on the web. The transactional capabilities open up the possibilities for collaborations across the internet. Users no longer need permissions to access the same spatial database, they can just use the standard WFS-T interface. This has the potential to truly enable open geo-data, just as the internet plus networked source code management tools enabled the open source movement.

Using Open Web Services

A. Introduction

B. Overview

C. WFS - Abstract Access to your Data

WFS - Abstract Access to your Data

D. WMS - Producing Maps

E. Building Web Applications

Appendix A. Projections and Coordinate Reference Systems

Appendix B. Glossary