Manual: DEM Surface Tools for ArcGIS
Last modified: January 19, 2013
Introduction:
This extension provides you with tools to generate a variety of surface characteristics of a
landscape, using both projected and unprojected (i.e. latitude / longitude) digital elevation model
(DEM) rasters. These tools include:
1) Surface Area and Ratio of a landscape
2) Slope, with 3 slope algorithm options
3) Aspect, with 3 aspect algorithm options
• This extension includes a tool to apply a traditional 9-category symbolization scheme
to an existing Aspect raster layer (Flat, North, Northwest, West, Southwest, South,
Southeast, East, and Northeast). This tool is useful if you load an aspect raster into
ArcMap and wish to classify it by direction.
4) Hillshade, with optional hypsometric tinting
5) Multi-directional Oblique-Weighted Hillshade, with optional hypsometric tinting
6) Seven types of Landscape Curvature
ArcGIS has many useful tools for calculating slope, aspect, hillshade and curvature from DEM
rasters. This extension offers some advantages over these existing tools in that:
1) These tools correctly handle Latitude / Longitude Data: The existing ArcGIS tools
typically do not work well with data in a geographic coordinate system (i.e. Latitude /
Longitude coordinates). They expect the vertical units of a digital elevation model to be
the same as the horizontal units, and at best they only allow you to enter in an
adjustment factor (generally called a “Z-factor”) to adjust your Z-units to your X/Y-units.
This Z-factor adjustment method is cumbersome to implement with latitude/longitude
coordinate systems because the correct Z-factor is both hard to calculate and changes
with latitude. Geographic data is especially confounding because the X-units are not the
same as the Y-units. Both are in “degrees”, but a degree in latitude (Y-units) is not the
same distance as a degree in longitude (X-units).
Unfortunately, most free elevation data available online is only available in
latitude/longitude coordinates. This data can be projected, but projecting raster data
introduces errors in resolution and precision (see horizontal and vertical artifacts on
illustration on next page). This extension modifies the algorithms used to calculate
common morphological characteristics of the landscape so that they accurately work with
latitude/longitude data without projecting the data or using Z-factor adjustments.
All methods are described in detail in the manual, but in general this extension will always
automatically detect the coordinate system of the raster and use the method appropriate
for that coordinate system.
2) These tools offer several options not available in the standard ArcGIS tools:
Including multiple slope and aspect algorithms, optional hypsometric shading for
hillshades, the MDOW model for hillshades, and many more options for landscape
curvature.
3) Surface Area and Ratio: This extension allows you to generate Surface Area and
Surface Ratio rasters from an existing Elevation raster. The cell values for these new
rasters reflect the surface area and (surface area) / (planimetric area) ratio for the land
area contained within that cell's boundaries. Surface Ratio provides a useful index of
topographic roughness and convolutedness, while Surface Area give a more realistic
estimate of the land area available than you can get from the simple planimetric area.
4) These tools do not require Spatial Analyst: This extension uses only standard ArcGIS
ArcObjects functions and therefore does not require a license for either Spatial Analyst or
3D Analyst.
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