# Surface Parameters

Available with Image Server

The Surface Parameters tool calculates parameters of a raster surface such as aspect, slope, and curvature using geodesic methods.

The output is a hosted imagery layer.

Learn how Surface Parameters works

## Examples

The Surface Parameters tool can be used in the following scenarios:

• Calculate aspect and slope using geodesic methods.
• Calculate different types of curvatures using geodesic methods. For example, you can calculate tangential curvature, which characterizes topographic convergence and divergence of flow across the surface.

## Usage notes

Surface Parameters includes configurations for input layer, surface parameter settings, and result layer.

### Input layer

The Input layer group includes the following parameter:

• Input surface raster is the surface raster that will be used for calculation.

If a z-unit is available in the vertical coordinate system of the input raster, it will be applied automatically. If the z-unit is undefined, Meter will be used by default.

### Surface parameter settings

The Surface parameter settings group includes the following parameters:

• Parameter type specifies the surface parameter type that will be computed.

Each available surface parameter type is calculated on a cell-by-cell basis by fitting a local surface around a target cell. The units of all curvature type outputs will be the reciprocal (the square of the reciprocal for Gaussian curvature) of the x,y-units of the output coordinate system. The available options are as follows:

• Slope—The rate of change in elevation, the first derivative of a DEM, will be computed. The range of values from the slope output depends on the unit specified for the Slope measurement parameter. This is the default.
• Aspect—The downslope direction of the maximum rate of change for each cell will be computed. The output represents the compass direction that the downhill slope faces for each location. It is expressed in positive degrees from 0 to 360, measured clockwise from north.
• Mean Curvature—The overall curvature of the surface will be measured. It is computed as the average of the minimum and maximum curvature. This curvature describes the intrinsic convexity or concavity of the surface, independent of direction or gravity influence. High positive values indicate areas of maximum denudation, and high negative values indicate areas of maximum accumulation (Minár et al., 2020).
• Tangential (normal contour) Curvature—The geometric normal curvature perpendicular to the slope line, tangent to the contour line will be measured. This curvature is typically applied to characterize the convergence or divergence of flow across the surface. Positive values indicate areas of diverging surface flow. Negative tangential curvatures indicate areas of converging surface flow. A positive tangential (normal contour) curvature indicates that the surface is convex at that cell perpendicular to the direction of the slope. A negative curvature indicates that the surface is concave at that cell in the direction perpendicular to the slope. A value of 0 indicates that the surface is flat.
• Profile (projected contour) Curvature—The geometric normal curvature along the slope line will be measured. This curvature is typically applied to characterize the acceleration and deceleration of flow down the surface. Positive values indicate areas of acceleration of surface flow and erosion. Negative profile curvature indicates areas of slowing surface flow and deposition. A positive profile (normal slope line) curvature indicates that the surface is convex at that cell in the direction of the slope. A negative curvature indicates that the surface is concave at that cell in that same direction. A value of 0 indicates that the surface is flat.
• Plan (projected contour) Curvature—The curvature along contour lines will be measured.
• Contour geodesic torsion—The rate of change in slope angle along contour lines will be measured.
• Gaussian curvature—The overall curvature of the surface will be measured. It is computed as the product of the minimum and maximum curvature. Positive values indicate that the surface is convex at that cell, and negative values indicate that it is concave. A value of 0 indicates that the surface is flat.
• Casorati curvature—The general curvature of the surface will be measured. It can be zero or any other positive number. It can be zero or always positive. High positive values indicate areas of sharp bending in multiple directions.
• Slope measurement specifies the measurement units that will be used for the output slope raster.

This parameter is only available if the Parameter type parameter is set to Slope. The available options are as follows:

• Degrees—The range of slope values is 0 to 90 degrees.
• Percent rise—The range is 0 to essentially infinity. A flat surface is 0 percent, a 45 degree surface is 100 percent, and as the surface becomes more vertical, the percent rise becomes increasingly larger.
• Project geodesic azimuths specifies whether geodesic azimuths will be projected to correct the angle distortion caused by the output spatial reference.

This parameter is only available if the Parameter type parameter is set to Aspect.

• Unchecked—Geodesic azimuths will not be projected. This is the default.
• Checked—Geodesic azimuths will be projected. In this case, north is always represented by 360 degrees and azimuths will be projected to correct the distortion caused by a nonconformal Output Coordinate System environment setting. These angles can be used to accurately locate points along the steepest downhill slope. Check the Project geodesic azimuths parameter if you are using the Surface Parameters tool output as a back direction input for the Input back direction raster parameter for a tool in the Use proximity toolset.
• Use equatorial aspect specifies whether aspect will be measured from a point on the equator or from the north pole.

This parameter is only available if the Parameter type parameter is set to Aspect.

• Unchecked—Aspect will be measured from the north pole. This is the default.
• Checked—Aspect will be measured from a point along the equator to correct for the skewing of direction that occurs when approaching the poles. This parameter ensures that the north-south and east-west axes are perpendicular to each other. Use this option if the terrain is near the north or south pole.
• Local surface type specifies the type of surface function that will be fitted around the target cell. The available options are as follows:

• Quadratic—A quadratic surface function will be fitted to the neighborhood cells. This surface function does not fit the neighborhood cells exactly, which is recommended for most data and applications. This is the default.

The quadratic surface minimizes the impact of noise in the input surface raster, which is especially important when computing curvature.

Use this option when specifying a neighborhood size through the Neighborhood distance parameter that is larger than the cell size and when using the adaptive neighborhood option.

• Biquadratic—A biquadratic surface function will be fitted to the neighborhood cells.

This option is suitable for a highly accurate input surface.

If the neighborhood distance is larger than the input raster cell size, the accuracy advantages of the biquadratic surface type will be lost. Leave the neighborhood distance as the default (equal to the cell size).

• Neighborhood distance is the distance from the target cell center from which the output will be calculated. It determines the neighborhood size.

The default value is the input raster cell size, resulting in a 3 by 3 neighborhood. It cannot be less than the input raster cell size. If a neighborhood distance is specified that does not result in an odd interval of the cell size, it will round up to the next interval of the cell size. In addition, the largest neighborhood distance is equal to 7 times the cell size, resulting in a 15 by 15 cell window. Any specified distance that is larger than 7 times the cell size will always result in using a 15 by 15 cell window.

A smaller neighborhood distance captures more local variability in the landscape, characteristics of smaller landscape features. With high resolution elevation data, larger distances may be more appropriate.

• Use adaptive neighborhood specifies whether neighborhood distance will vary with landscape changes. The neighborhood distance will shrink if there is too much variability in the calculation window. The maximum distance is determined by the value of the Neighborhood distance parameter.

The minimum distance is the input raster cell size.

• Unchecked—A single (fixed) neighborhood distance will be used at all locations. This is the default.
• Checked—An adaptive neighborhood distance will be used at all locations.
• Z unit specifies the linear unit of vertical z-values.

It is defined by a vertical coordinate system, if it exists. If a vertical coordinate system does not exist, the z unit should be defined from the unit list to ensure correct geodesic computation. The default is Meter. The available linear units are Inch, Foot, Yard, Mile US, Nautical mile, Millimeter, Decimeter, Centimeter, Meter, and Kilometer.

### Result layer

The Result layer group includes the following parameters:

• Output raster name is the name of the raster that contains the specified surface parameter type values.

The name must be unique. If a layer with the same name already exists in your organization, the tool will fail and you will be prompted to use a different name.

• Save in folder specifies the name of a folder in My Content where the result will be saved.

## Environments

Analysis environment settings are additional parameters that affect a tool's results. You can access the tool's analysis environment settings from the Environment settings parameter group.

This tool honors the following analysis environments:

## Outputs

The output is one output raster with the specified surface parameters type values.

## Licensing requirements

This tool requires the following licensing and configurations:

## References

• James D.E., M.D. Tomer, S.A. Porter. 2014. "Trans-scalar landform segmentation from high-resolution digital elevation models." Poster presented at: ESRI Annual Users Conference; July 2014; San Diego, California.
• Minár, J., Evans, I. S., & Jenčo, M. 2020. "A comprehensive system of definitions of land surface (topographic) curvatures, with implications for their application in geoscience modelling and prediction". Earth-Science Reviews, 103414. https://doi.org/10.1016/j.earscirev.2020.103414