In this exercise, we will create a new web map using the ArcGIS Online map viewer. The SaaS service model specifically enables access to resources from a thin client (e.g., Web browser) and conceals the underlying cloud infrastructure, including network, servers, operating systems, and storage. The following example of building a map in ArcGIS Online takes this service model one step further by integrating not just the services of one cloud computing infrastructure (Esri), but also the underlying infrastructures of other cloud services as well (US Census Bureau, NOAA). You'll see how ArcGIS Server services can be mixed with other types of services, such as WMS, during this process.
Let's take this opportunity to review the Essential Characteristics of Cloud Computing and identify how services like ArcGIS Online achieve them:
- On-Demand self-service. Cloud computing resources should be accessible anytime and without the need for human interaction with the service provider. Like most websites, ArcGIS Online is accessible via a browser 24/7 without the need to request permission.
- Broad network access. The capabilities of ArcGIS Online are accessible from any location via the Internet, using ubiquitous clients, such as Web browsers.
- Resource Pooling, Rapid Elasticity and Measured Service. These characteristics are hidden from the client in a SaaS service model. In the case of ArcGIS Online, the allocation of resources to client requests is performed automatically by the underlying cloud infrastructure without knowledge of the user. This characteristic is of particular relevance to map services, like those you created using ArcGIS Server. The configuration of every map service specifies the maximum number of instances that service can instantiate. If multiple users request a service concurrently, additional instances can be generated to handle the simultaneous requests. If the server architecture includes multiple physical or virtual servers, map service instances can be created and destroyed on any of the available servers in a way that balances the processing load. This occurs automatically without any human interaction in the client or server.
To illustrate the flexibility and interoperability of cloud GIS, we will consume three map services from various service providers via different protocols (Esri GeoServices REST Specification and WMS). You can then add more services to this map if you wish, including any services you have published in earlier exercises. For now, let’s consume an Esri basemap service via REST, a glaciers layer via WMS, and a snow depth layer via REST. We’ll imagine that we are planning a hiking trip in Mount Rainier National Park, and we want to get an understanding of conditions.
First, download the data for this lesson. Then, do the following:
- Open arcgis.com in your web browser, and log in using your Penn State Enterprise account that you created previously in this course.
- Click Map.
- Click Basemap, and select Dark Gray Canvas.
When you consume a map service, you often don’t get much control over the symbology, other than the transparency level. The layers we’re going to consume are lightly colored, so we’ll use the dark basemap. This particular basemap also tends to mute out most layers and this is a good thing for our map; it will keep things uncluttered.
Let’s start by adding a map served through the WMS (Web Map Service) specification. WMS is a vendor-neutral set of request and response syntax specifications defined by the Open Geospatial Consortium (OGC) for serving rasterized map images drawn on demand. Many government organizations (especially in Europe) make their web services available through WMS.
- Open a new web browser page or tab, and browse the WMS services made available through the US Census Bureau TIGERweb We’ll add the one for Physical Features, so take note of that one’s URL.
- In your arcgis.com map viewer, click Add > Add Layer From Web.
- From the dropdown list, choose A WMS OGC Web Service.
- Enter the URL, which should be something like https://tigerweb.geo.census.gov/arcgis/rest/services/TIGERweb/tigerWMS_P...
Interestingly, you will often see “arcgis” in the URL of WMS services. This just means that the organization is using ArcGIS Server to power the service, but they have checked a box in the software to make the service available through the WMS specification in addition to Esri’s GeoServices specification. The back end data doesn’t change: just the way that it is requested and returned.
You may also need to add "WMSServer" to the end of the URL to indicate that you want to consume the service using that protocol instead of REST.
- Click Add Layer and wait a minute for the layer to appear on the map. It may take a few seconds to draw. Remember that this service is being drawn at the time you request it; it is not cached. Don’t zoom and pan around while you are waiting, as this will generate more requests and hold up the server even more.
If you don’t see anything at first, zoom in to a more local scale.
- In the left hand table of contents, expand tigerWMS PhysicalFeatures. Notice all the layers available. We’re just going to use this service to view glacier coverage.
- Uncheck all layers except Glaciers and its parent node Hydrography.
- Zoom to the Mount Rainier area in central Washington state. Use the search box if you need to.
You should be seeing various glaciers covering the mountain.
- Open a new tab or window in a web browser and examine this ArcGIS Services Directory metadata page for a snow analysis service made available through the National Weather Service:
- In the arcgis.com map viewer, click Add > Add Layer From Web.
- Choose An ArcGIS Server Web Service from the dropdown, and enter the same URL as two steps above.
- Click Add Layer and examine the snow depth layer. If you’re interested in what the color ramp means, you can click the Legend button on the left hand side. I wasn’t able to find the units in the metadata, and there was hardly any snow in the US in August when I wrote this, but the units should become clearer in the winter using some common sense.
- Make the snow analysis layer somewhat transparent by clicking the … beneath its name in the contents and clicking Transparency. You want to make it transparent enough that you can see the glaciers beneath.
- Save your map as Hiking Conditions.
You just assembled a web map by combining web services from multiple sources. In the next section of the lesson, you'll add in some of your own data.