How to classify a map or column

You can:

1. Slice or classify a value map interactively;
2. Slice or classify a value raster map permanently;
3. Classify a value column permanently;
4. Perform a multi-spectral image classification on satellite imagery.

1. To slice or classify a value map interactively:

• Double-click a value map (raster, polygon or segment map) in the Catalog;
• In the Display Options dialog box, click the create button next to the Representation list box;
• in the appearing Create Representation dialog box, type a name for the new representation but do not change the domain listed in this dialog box;
• when the map is using the system domain Value, you will create a representation gradual, in which boundary values are represented by percentages;
• when the map is using any other value domain, you will create a representation value in which boundary values are the actual values in your map;
• Click OK in the Create Representation dialog box. The Representation Value/Gradual editor is opened;
• Click OK in the Display Options dialog box of the map. The map is displayed in a map window;
• Keep the map window open and switch to the editor.

Tip:

For maps which use system domain Value, only a representation gradual can be created which works on percentages. When you want to create a representation value (working on values) for such maps, you need to change the domain of the map from system domain Value to a user-defined value domain. For more information, see How to change the domain of a map.

• In the Representation Value/Gradual editor, you can add limits, assign colors to the limits, and choose to stretch in between limits or use the colors of upper or lower boundaries (slices);
• to insert a limit: choose Insert Limit from the Edit menu or press Ins on the keyboard; in the appearing Insert Limit dialog box, type a value for the upper boundary of a slice, e.g. 100 and assign a color to this limit;
• double-click a number of times in between two limits, and decide whether the color(s) of the values in between these two limits in the map should be stretched or should use the color of the upper limit or the lower limit;
• double-click an existing limit to change its boundary value or its color;
• the color bar at the bottom of the editor gives an impression of how your total representation looks like;
• When finished adding limits, keep the Representation editor open, and switch to the map window;
• In the map window, click the Redraw button in the toolbar. The map will be displayed in the colors you just defined;
• Keep the map window open and switch to the representation editor.
• Continue to edit boundary values and/or colors in the Representation Value/Gradual editor, and redrawing the map window until satisfied.

For more information, see also ILWIS objects : representations, Representation Value/Gradual editor or How to slice an image.

2. To classify a raster map with a value domain permanently:

• You can first try the interactive method;
• Create a domain Group (Main window, File, Create) in which you fill in the upper boundaries and the output class/group names. For more information, see How to create a Group domain.
  Optionally, you can edit the representation for this domain, by choosing the Representation command from the Edit menu in the domain editor.
• Then, in the Main window, open the Operations menu, choose Image Processing, Slicing or use the CLFY function on the command line of the Main window or in a MapCalc dialog box. For more information, see the Slicing operation or Map calculation : classifying a map (CLFY).
• Display the output raster map in a map window.
• You can edit the representation of the map by choosing the Representation command from the Edit menu in the map window. Redraw the map in the map window.

To edit the representation of the classified map:

• In the map window, open the Edit menu and choose Representation;
• The Representation Class editor is opened: edit the colors of the classes as you wish;
• Keep the editor open and switch to the map window;
• In the map window, click the Redraw button.

You can continue switching to the Representation editor and back to the map window to redraw the map until satisfied.

To change the boundary values on second thought:

• You may keep the map window open;
• In the map window, open the Edit menu and choose Domain;
• The Domain Class/ID/Group editor is opened: edit the boundary values of the groups, insert more groups, etc.;
• In the map window, open the Edit menu and choose Properties;
• In the appearing Properties dialog box, click the Make Up-to-Date button;
• a message appears asking for confirmation to recalculate the map, click OK;
• when the calculation has finished, click the Redraw button in the map window.

3. To classify a column with a value domain:

You can choose to work via a dialog box or via the command line of the table window.

When you wish to work through a dialog box:

• choose Column Slicing from the Columns menu in the table window;
• the Column Slicing dialog box will appear;
• you can create a domain Group which contains upper boundary values and output class names via the dialog box.

When you wish to type a formula on the command line:

• create a domain Group in which you fill in the upper boundaries and the output class/group names;
• use the CLFY function on the command line in a table window:

 

    OutputColumn = CLFY(InputColumn, GroupDomain)

For more information, see Map & Table calculation : CLFY function.

4. To perform a multi-spectral image classification on satellite imagery:

• create a sample set of the bands with Sample, and the Sample Set editor;
• open the Operations menu, choose Image Processing, Classify.

For more information, see Sample, Sample Set editor, and Classify.