# Surface Parameters function

Available with Spatial Analyst license.

## Overview

Determines parameters of a surface raster such as aspect, slope, and several types of curvatures using geodesic methods.

For more information, see the How Surface Parameters works topic in the Spatial Analyst tool help.

## Notes

This function can be used for the following applications:

• Calculate aspect and slope using geodesic methods.
• Calculate different types of curvatures from an input surface raster, for example, Tangential (normal contour) curvature which characterizes topographic convergence and divergence of flow across the surface.

## Parameters

Parameter nameDescription

Raster

(Required)

The input surface raster. It can be an integer or a floating-point raster.

Parameter Type

Specifies the output surface parameter type that will be computed.

• Slope—The rate of change in elevation will be computed. This is the default.
• Aspect—The downslope direction of the maximum rate of change for each cell will be computed.
• 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.
• 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.
• Profile (normal slope line) 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.
• 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.
• Casorati Curvature—The general curvature of the surface will be measured. It can be zero or any other positive number.

Local Surface Type

Choose the type of surface function that will be fitted around the target cell.

• Quadratic—A quadratic surface function will be fitted to the neighborhood cells. This is the default type.
• Biquadratic—A biquadratic surface function will be fitted to the neighborhood cells.

Neighborhood Distance

The output will be calculated over this distance from the target cell center. It determines the neighborhood size. The default value is the input raster cell size, resulting in a 3 by 3 neighborhood.

Specifies whether neighborhood distance will vary with landscape changes (adaptive). The maximum distance is determined by the neighborhood distance. 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

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.

• Inch—The linear unit will be inches.
• Foot—The linear unit will be feet.
• Yard—The linear unit will be yards.
• Mile US—The linear unit will be miles.
• Nautical mile—The linear unit will be nautical miles.
• Millimeter—The linear unit will be millimeters.
• Centimeter—The linear unit will be centimeters.
• Meter—The linear unit will be meters. This is the default.
• Kilometer—The linear unit will be kilometers.
• Decimeter—The linear unit will be decimeters.

Output Slope Measurement

The measurement units (degrees or percentages) that will be used for the output slope raster. This parameter is only active when Parameter type is Slope.

• Degree—The inclination of slope will be calculated in degrees. This is the default.
• Percent rise—The inclination of slope will be calculated as percent rise, also referred to as the percent slope.

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 active when Parameter type is Aspect.

• Unchecked—Geodesic azimuths will not be projected. This is the default.
• Checked—Geodesic azimuths will be projected.

Use Equatorial Aspect

Specifies whether aspect will be measured from a point on the equator or from the north pole. This parameter is only active when Parameter type is Aspect.

• Unchecked—Aspect will be measured from the north pole. This is the default.
• Checked—Aspect will be measured from a point on the equator.