FAQs for World Elevation services

Note:

BETA NOTE: Access to the World Elevation services is limited. If you want to join, sign up with Esri's Beta Community World Elevation Services beta program.

What client software applications can use these elevation services?

• ArcGIS Software (10.0 and later) can connect and use these image services.
• Any web application compatible with standard protocols, such as Esri's open REST and SOAP standards, as well as OGC standards (WMS for all services and WCS for a limited selection of services).
• For effortless viewing of the services with metadata, you can use a web browser.

Viewing and using the World Elevation services

Connecting client software to the World Elevation services requires authentication (login and password) using an Esri Global account. Some client software does not properly process authentication for these services. See the steps below to connect to the services in ArcGIS Desktop, the ArcGIS Online map viewer, and ArcGIS Explorer Desktop.

Connecting within ArcMap

Steps:

1. Open ArcMap.
2. Open the Catalog window.
3. Within the Catalog window, expand GIS Services and double-click Add ArcGIS Server.
4. Choose Use GIS Services and click Next.
5. Enter the Server URL, http://elevation.arcgisonline.com/arcgis/services, and your Esri Global User Name and Password, then click Finish.

   The Catalog window will display the WorldElevation folder, which contains numerous World Elevation services.

   If you are not a member of the World Elevation Services (BETA) group, you will not be able to access these services. To join, sign up with Esri's Beta Community World Elevation Services beta program.

Connecting with the ArcGIS Online map viewer

Steps:

1. Go to ArcGIS.com and sign in.
2. Click Groups at the top of the window.
3. Navigate through your list of groups and click World Elevation Services (BETA).

   If this is not listed, then you have not joined the group. To join, sign up with Esri's Beta Community World Elevation Services beta program.

4. To access the image services, look for the ones identified as an Image Service.
5. Click the Open arrow and click Open in ArcGIS.com map viewer.
6. The web viewer will open, and you will see a security warning. Click No.

   If you select Yes, you will be unable to see the image service.

7. You will be prompted to sign in. Enter your Esri Global account and password.

   The image service will load into the web viewer.

Connecting within ArcGIS Explorer Desktop

Steps:

1. Start ArcGIS Explorer Desktop.
2. On the Home tab, click Map > Add Content > GIS Services.
3. In the Server text box, enter the URL of the World Elevation services: http://elevation.arcgisonline.com/arcgis/services.
4. Enter your user name and password and click Next.
5. Choose a service from the directory of services and click Add Service.

   The new layer will appear in the table of contents.

   Remember, some services are for visualizing elevation data, such as SlopeMap or Hillshade. If you want elevation data values, use DSM, DTM, DTMEllipsoidal, or TopoBathy.

6. If the data is the elevation data values, you can use it for 3D viewing by changing ArcGIS Explorer Desktop in 3D mode.
   1. On the Home tab, click Map > 2D/3D > 3D Display.
   2. Right-click the elevation layer in the table of contents and click Properties.
   3. Click the Layer Type node and click Use it as an elevation source.
   4. Click OK to close the dialog box.

Do I have to pay to use these services?

These image services are free for noncommercial use or for development and testing. The data comes from numerous public domain data sources, such as GMTED at 1 km resolution, SRTM at 90-meter resolution, USGS NED data, and others. If you are interested in the commercial use of these services, please refer to the Web Services and API Terms of Use at http://www.esri.com/legal/pdfs/e-800-termsofuse.pdf.

Can I access the actual elevation values, or are these just pretty pictures?

These image services provide access to the elevation values and nice-looking imagery. They are distinguished as image services for analysis—the actual values—or image services for visualization—the nice-looking imagery. See the Image services table to learn about each image service.

Where did this elevation data come from?

Source data for Esri's World Elevation services comes from a variety of authoritative sources, as summarized in this table. Refer to the online metadata for more detail.

Sources	Data	Approximate Cell Size (m)
www.oregonmetro.gov	Portland lidar DEM	0.9
www.intermap.com	Intermap DEM	4.6
www.usgs.gov	NED 2, 1, 1/3rd, 1/9th Arc Second DEM	62 - 3.1
www.usgs.gov www.cgiar-csi.org www.nasa.gov	SRTM DEM	93
www.usgs.gov	GMTED DEM	232
www.bodc.ac.uk	GEBCO Bathymetry	928
earth-info.nga.mil	EGM2008	4638

Data sources

What is the spatial resolution of the elevation data?

This elevation data is comprised of multiple sources, at different resolutions and different geospatial extents. See the table above for more information.

What is the accuracy of the data?

The World Elevation services on ArcGIS Online are based mostly on public domain data (with exceptions in small areas, currently from Intermap and Oregon Metro). As an example, the USA is covered by 31-meter (1 arcsec) and 10.3-meter (1/3 arcsec) resolution data from USGS NED, with some areas also showing 3.1 meter (1/9 arcsec)—but the accuracy varies according to several factors:

• By data source—This depends on the dataset you’re accessing (for example, at a scale of approximately 1:400,000 the server will return SRTM data).
• By region—Some of the data was compiled from multiple sources (for example, GMTED and GEBCO), and accuracy will vary by location, depending on the original source.

Accuracy metadata for individual raster datasets is available in some cases (with more to come in later releases). Today, the metadata is resolved only to the full dataset, such as for all of the NED 10.3-meter data.

If you query the attribute table for any dataset, the fields LE90 and CE90 provide estimates of the linear error (vertical) and circular error (horizontal), respectively.

What is the difference between orthometric height and ellipsoidal height?

Orthometric height refers to elevation values above or below a geoid model surface; the geoid approximates local sea level. Although the geoid is also a mathematical surface that is relatively smooth, it includes much more variation than the ellipsoid, caused by local differences in gravity. For traditional (nonsatellite based) surveying methods, all measurements are generally made relative to the geoid (local sea level).

• Ellipsoidal Heights are typically used for applications based on GPS data, and for orthorectification of satellite imagery, whereas aerial photography can use either depending on the datum used for the exterior orientation. The exterior orientation can be either orthometric (if the control for the project was generated using ground station data) or ellipsoidal (such as airborne GPS + IMU). In the latter case, ellipsoidal ground height would be required to support the orthorectification process.
• Orthometric Heights are typically used in surveying, hydrology, agriculture, and land management.

When I load the slope into my display (Desktop or Online map) it is all black. Is that correct?

Although it can be confusing, that result is correct for the World Elevation Slope image service at very small scales (such as viewing the entire world or an entire continent). The Slope image service returns numeric values from 0 to 90 degrees and is not intended for visualization.

You can change the layer properties in ArcMap to stretch the histogram to provide some contextual information (to highlight rugged terrain and allow you to identify landmarks), but adding a basemap or the Slope Map image service are better methods.

Also note that, at small scales (smaller than 1:250,000), the resampled spatial resolution of a single pixel on screen makes the concept of slope somewhat meaningless. Esri considered disabling these services at small scales, but a blank screen can also be confusing for users. Use the World Elevation Slope Map image service if you require a useful visualization of slope, and use the World Elevation Slope Map image service at larger scales when numeric values are appropriate.

Why do I get an error or black image when I export?

The World Elevation services limit the size of image you can export from them to 4000 by 4000 pixels. With ArcGIS 10.0 SP4 and higher, you will receive an error message when attempting to export an area exceeding this limit. However, if using an earlier version you may end up with a black image.

You can see the size on the Export dialog box in the Raster Size (columns, rows) text boxes. The estimated numbers will be populated in these text boxes even this option is not selected.

To change the values you can modify your extent by using a graphic to clip the image service, or modify the other parameters on this dialog box, such as the Cell Size or the Raster Size.

When changing the Raster Size, check Square to keep the Cell Size dimensions the same.