![[logo] US EPA](http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Web Mapping Services Help and FAQ
Overview
The EPA Office of Water has made available several Web Mapping Services that contain nearly all of the NHD-based WATERS Program data, plus other WATERS-related layers. The services are available for use from the EPA's intranet and internet environments. This purpose of this help page is to provide 'how to' information for both general users and application developers.
Determine the WATERS mapping services you wish to consume:
The complete list is located at WATERS mapping services.
Determine the mapping service format best matching your needs:
WATERS mapping services are provided in a variety of formats for the widest possible public usage. Depending on your needs and client software, certain formats are better than others for specific tasks. See the discussion at WATERS mapping services. In general, image-based services are best for tasks displaying complex but non-interactive cartography while feature-based services provide much-enhanced functionality to select and analyze features at the expense of performance.
Determine your service endpoints and inspect layer metadata
Use of any service requires knowing the endpoint for the service. EPA mapping services are described and their access endpoints detailed via their entries at the Geospatial One-Stop. Search for the service name using the search feature to discover metadata and access information regarding the service.
Accessing WATERS mapping services from ESRI
desktop software
From ESRI commercial desktop applications (ArcMAP, ArcCatalog), you will be able to access ArcIMS image and feature, ArcGIS map, and WMS services directly. ESRI ArcExplorer can access ArcIMS image, ArcGIS map and WMS services.
- Select the 'Add Layer' button
- Select the type of server containing the services you wish to consume.
ArcIMS for ArcIMS Image and Feature Services
WMS for OGC WMS Services
ArcGIS Server for ArcGIS Map services
- Enter the address for endpoint as defined on the Geospatial One-Stop
- Once you see the service name listed to the right, highlight it and press the 'add' or 'open' button
This service and all of its available layers are now loaded into your mapping application.
Here is an example of an ArcIMS image services list viewed with ArcExplorer
If the layers in the services are scale dependent, you may not see all the layers listed in the table of content (TOC) in the map window. If you cannot see the layers you are interested in, you probably need to zoom in or zoom out until the layers' legends become active in the TOC. Once the layers become active, select the layers to display them in the map window. You may also need to scroll down TOC panel to see all the layer names.
When drawing a large number of layers, or a layer with large number of features, you may need to wait for several seconds to get the layers drawn in the map window. After the layers are selected to draw, a green flashing light in the upper-left corner of the TOC indicates that the application server is working to generate a new map. Once loaded, individual layers can be turned 'on' or 'off' by checking or unchecking the checkboxes at the left of the layer names in the TOC.
Unlike an image service, each individual layer in a feature service is added separately into the ArcGIS Desktop application after the service is selected. Another advantage of the feature service is that you can customize the symbology of each map layer.
These services can be used in conjunction with data from other sources (including local data sources). However, in that case, symbology conflicts may exist, and filled polygon layers may hide other layers; these issues will have to be assessed and solved by the user on a case-by-case basis.
Accessing WATERS mapping services from third-party and open source
clients
Almost all third-party and open source clients software utilize OGC open standards to consume and display mapping services. Currently, OGC WMS is the only such standard available for WATERS services.
Quantum GIS
Then choose the individual layers required.
And then use the layers similarly to any other image layer in your application.
A more complex open source client is the Open Layers
var wms_layer = new OpenLayers.Layer.WMS(
"RAD BASIC WMS",
"http://indusdemo.induscorp.com/wmsconnector/com.esri.wms.Esrimap/RADBASIC_IMAGE?service=WMS&version=1.1.1",
{
layers: '0,12,15'
srs: 'EPSG:102113',
transparent: true,
format: 'image/png'
},
{ isBaseLayer: false }
);
my_map.addLayer(wms_layer);
Many other open source and third party clients are available beyond these examples. The only restriction is they must conform to the open source specifications published by the Open Geospatial Consortium
General Information/FAQs
What is WATERS?
See Watershed Assessment, Tracking & Environmental ResultS.
What is the RAD?See Reach Address Database Documentation.
Why can't I see all the layers in a WATERS mapping services?
The map layers available in WATERS mapping services can be extremely large. For example, an attempt to draw all of the NHD Waterbodies at the national scale/level may fail because it contains too many features to render, which may cause the web server to time out. Not to mention, even if the features do draw, they would be so dense that virtually nothing would be discernable on the map. The same situation occurs in EnviroMapper, which only permits the layers with a big number of features to be drawn when zoomed in to the 'state' or 'local' scale. WATERS mapping services use a similar approach to set 'scale thresholds' for each layer. These scale dependencies will not permit a layer to display until the map is zoomed in to the point where the scale threshold is crossed. If a layer is not visible, keep zooming in until the layer becomes active in the TOC. (Note: you may have to scroll down the TOC to see all of the available layers). Once the layer is available in the TOC, you can click the check box to turn it 'on' if it isn't already checked. If you still don't see any of that layer's features on the map, it is because there are no features in the part of the country that you are viewing.
The RAD IMS Scale Thresholds are designed to match the "National", "Regional", "State", and "Local" thresholds set in EnviroMapper for Water. Labels are also associated with scale dependent layers. The more you zoom in, the more labeled features will be visible.
Why are there 'Empty' Layers available in RAD Program Services?
Each RAD program layer feature type is really comprised of three logical layers: 'points', 'linear', and 'area'. To be sure that you are viewing all of the data for a program layer, all three feature types need to be turned on. Some RAD programs may not have data for all three feature types, but however, the non-existent feature types have also been added to the services as empty layers being the place holders so that as soon as the data is available the features will be automatically available to map.