To find the highest slope within a area around a point, blank the grid to the desired radius, and view the grid info.
- Create the slope grid file.
- Click Grids | Calculate | Calculus.
- In the Grid Calculus dialog, select a map using your grid file from the Input Grid dropdown list, or click the Browse button to navigate to and select your grid file.
- Choose Terrain Modeling | Terrain Slope.
- Change the Output Grid name and location, if desired.
- Uncheck the box next to Add grid as layer to.
- Click OK and the grid is created. (Click OK in the Surfer dialog telling you the grid was created.)
- Now create a BLN defining the area you want to calculate the maximum slope in. Please see this article for instructions to create a BLN file. If you have Surfer 14, you can easily create the circular area around a point in a base layer using the Features | New Features | Buffer command.
- Click the Grids | Edit | Blank command.
- In the Grid Blank dialog:
- Select a map using your grid file from the Input Grid dropdown list, or click the Browse button to navigate to and select your grid file.
- Select a map using your BLN file from the Blanking Polygon Boundary dropdown list, or click the Browse button to navigate to and select your BLN file.
- Toggle the appropriate option for the direction of blanking (inside, outside, or mixed).
- In the Output Grid field, enter a name for the new blanked grid.
- Uncheck Add grid as layer to.
- Click OK.
- Click the Grids | Info | Grid Info command.
- Select the blanked grid file created above and click Open.
- In the Grid Information report, scroll down to the Univariate Grid Statistics section. The Maximum is the maximum value in the non-blanked portion of the grid.
For additional statistics about the slope in this radius, you can:
- Convert the GRD file to a DAT file (Grids | Edit | Convert).
- Open the DAT file in the worksheet (File | Open).
- Sort on Column C (Data | Data | Sort).
- Remove the rows with NoData values (1.70141e+038).
- Select the desired data cells.
- Click the Data | Data | Statistics command.
- Check the boxes next to the desired statistics.
- Click OK to calculate those statistics for the selected cells.
Updated January 9, 2017