Pitney Bowes MapInfo Vertical Mapper - Manual (Page 129)

Chapter 7: Using Grids for Spatial Analysis
User Guide
127
Understanding Slope and Aspect
As it applies to grid geometry, slope is a measurement of the “steepness” of a grid cell in three-
dimensional space and is therefore most applicable to elevation surfaces. In Vertical Mapper, slope
is calculated by averaging the slopes of the eight triangle faces that are formed from the surrounding
nodes.
Aspect measures the direction that each grid cell faces in three-dimensional space and is recorded
in azimuth degrees relative to either true north or the top of the map. In Vertical Mapper, aspect is
calculated by averaging the aspects of the eight triangle faces that are formed from the surrounding
nodes.
The eight triangles are created to determine the slope at node “A”.
Creating Slope and Aspect Grids
Vertical Mapper enables you to create the slope and aspect for a grid file. The Z-units of the grid
must be linear units.
1. In the Grid Manager, click the Analysis button and choose the Create Slope & Aspect
command.
2. In the Slope and Aspect dialog box, choose a grid from the Grid list.
3. Enable the Create Slope Grid check box to create a slope grid.
4. Enable the Calculate as % Grade check box to calculate the slope as a percent grade. When
you clear this check box, the slope is calculated in degrees.
5. Enable the Create Aspect Grid to create an aspect grid.
6. In the Aspect Parameters section, do one of the following:
• Choose the Calculate Aspect Relative to True North option to set north to zero degrees
azimuth and allow values to progress in a clockwise direction.
• Choose the Calculate Aspect Relative to Y-axis option to set “Y” at the top of the map.
7. In the Description boxes, enter descriptions (maximum 31 characters). The descriptions will be
carried as a header in the new grid file.
8. In the File name boxes, enter a file name for each grid to be created.
9. Click the OK button.