Monday, July 1, 2013
AGOL, Web Services, and Mashups
My next foray with Arc GIS Online is to explore some the available web services that can be added to AGOL and how they might be used. Many of the maps and web services I work with are national status maps or inventories. The search for available services started when I wanted to add labels on county polygons for one of my web applications.
Web Services Terms
Skip this section if web services are second nature to you. Some of the nuances among these terms are important to understand for AGOL. WMS is a Web Map Service. This is a completed map provided with symbology and scale visibilities, essentially providing an image of the map. Within AGOL a single web service may have multiple layers that can be turned on and off, and have customized popups. In AGOL these are added as A WMS OGC Web Service.
WFS is a Web Feature Service. This service provides the actual features, not a map image of them. Features can be analyzed, downloaded, added to a desktop canvas, and are typically provided in an extensible markup language (XML) for geography (GML). This means the definitions of the features are provided and the features can be added to a variety of software platforms. AGOL does not have the capability to add WFS, but links to the WFS for a feature could be added to the customized popup, if you wanted to provide information on the WFS address.
REST or RESTful Services is a Representational State Transfer (did that clarify the term?) and this is another standard or architecture for providing access to web served data and services. In AGOL these services are added as ArcGIS Server Web Service. The transparency and visibility ranges (minimum and maximum display scale) can be configured for Restful Services in AGOL.
There are many WMS, WFS, and REST Service available to supplement your AGOL map. I did a web search from my browser, but there is also a search engine within the AGOL map to find available services.
These are fairly easy to add to any map, just add data from the web and select the type of service. The service adds fairly quickly, if you pick the right type. After the service appears on your map, click on the service in the details information on the map viewer and the layers within that service can be added and configured individually.
Since county labels were my first requirement I started with Tiger Web. http://tigerweb.geo.census.gov/tigerwebmain/TIGERweb_wms.html
This WMS had exactly what I needed for state and county labels as well as American Indian Areas with labels. School districts and federal congressional districts are also available along with many of the Census geography features. This service provides a lot of rich Census content as well and it is an easy way to display place names and geography with some population information. The geography and the labels are offered separately and the labels scale nicely. The WFS services on Tiger Web are really helpful to view your current Census geography with your local data sets on an ArcGIS desktop map canvas as well. No need to download and re-project the Census geography files. This is for desktop, not AGOL.
The National Map Web Services is another fairly easily navigated web site to find services. http://viewer.nationalmap.gov/example/services.html
This site has a good variety of imagery, elevation, and federally managed data sets available as WMS and WFS. All of the links worked and the data added as advertised.
There are a lot of map and feature service available at the federal Geospatial Platform. Finding the available WMS and WFS services is not particularly obvious at this site but a search for WMS found 26 results on the Geoplatform and 1,043 harvested items. However, many of these did not work as advertised, some had data in them some did not, some were web services and some were viewers only, but it’s a start. Many states also have some excellent web services. Montana and Arkansas are two states I have used.
It is interesting to add the same data from different web service sources and see the differences in the representations. State, county, and city boundaries have a variety of representations and all seem to be sourced differently. I suspect as the use of the web services because more accepted there will more reliance in single authoritative representations of commonly used layers.