Overview

This section of the Image Management Guidebook provides guidance specific to managing and serving elevation data (including forms such as bathymetry, bare earth and first return surfaces from lidar, and so on).

This guidebook also provides an overview of how the ArcGIS World Elevation Services were created. The World Elevation services provide access to multiple representations of multiresolution, multisource global elevation data that are accessible as image services. Over time, these services will be extended with additional datasets contributed as part of the community map program. Organizations will want to implement similar services internal to their organizations utilizing similar datasets or using their own elevation data sources. This guidebook provides the details on how to implement such services.

This Elevation section of the Image Management Guidebook will follow the same structure as the Common workflow steps in the previous section of the guidebook.

Most of the recommendations in this document have been implemented in the sample scripts available for download and user modification in the ArcGIS Image Management Workflows group on ArcGIS Online. It is recommended that these scripts and sample data be downloaded and reviewed in conjunction with these workflows, as they provide ways to automate the generation of such services and implement many of the best practices defined here.

Considerations regarding usage modes for elevation

Due to the potentially large data volumes and complexity of working with elevation data, most users do not want to download and directly work with the original elevation data files, but prefer instead to connect to services that provide the required information derived from authoritative sources.

There are three different modes for access to elevation data:

Visualization

Many end users simply need to see visualizations of the topography to meet their needs. They often want to understand the topographic context of the area such as the location of higher ground.

They are interested in representations such as the following:

• A hillshade image (grayscale or elevation tinted) for inclusion in a topographic map or basemap.
• An image representing slope for urban planning, landslide susceptibility, and so on.
• An image representing aspect for agriculture, wildlife management (habitat delineation), climate modeling, and so on.

In such cases, they do not need the actual elevation data, but their needs are met by the server transmitting the required representations back to them.

Analysis

Some users would want the results of some kind of topographic analysis overlaid on a map or used as part of a subsequent analysis, and not necessarily the original data. They are interested in the answers to questions such as the following:

• Extent of flood plain—For FEMA, insurance companies, city/county government, real estate, disaster management, and so on
• Viewshed calculations, for visibility and line-of-sight analysis—"What can be seen from this point?" for siting cell phone towers and microwave communication equipment, for planning clear cuts, and so on
• Calculation of profiles along straight lines or line segments—For engineering pipeline routes and pressure calculations, road planning, timber harvest planning (road planning and extraction cost), and so on

Such processes are best answered by services that perform the analysis on the server and return only the required geometries. Again, the data need not be downloaded, but typically the server application that performs the analysis needs access to comprehensive services that can provide the required elevation.

Data values

There is a group of users that may require access to the actual elevation values, typically to do their own analysis. In many cases, they may prefer to obtain a derived data product versus the actual elevation value, for example, a slope analysis to be used in terrain analysis or a mask to be used for identifying areas with high avalanche potential. Such derived data products are often significantly smaller in volume than the original data. Some users, though, do require the original data values. Transmitting the original data values is most expensive in terms of data bandwidth, so it should be applied only when necessary.

By managing elevation data using mosaic datasets and serving image services and associated geoprocessing services, these three usage modes can be effectively addressed. This section of the guidebook will provide details on how to create and serve such mosaic datasets.