Theme Creation and Digitizing Tools

Creating a theme and using the digitizing tools

Once a classification scheme has been loaded, this button will create an empty theme (select either a polygon, line, or point theme) with the appropriate fields. If a default legend has not been created using "Habitat Digitizer/Set Default Legend" or the "Change Classification" dialog, a dialog will appear to select a legend file. A second message box will appear asking if this legend should be made the default legend for all new themes created using this classification scheme.

To start digitizing a new polygon, select this tool and trace the feature of interest by clicking around its perimeter with the mouse. A double click closes each new polygon. If a polygon is digitized inside or completely around an existing polygon, "donut" and "donut hole" polygons will be formed. Once the polygon is complete, a message box will allow the classification to be set as outlined below.

Use this tool to add a polygon adjacent to an existing polygon. To create a polygon using this tool, start tracing a line inside of the adjacent polygon and end the line by clicking twice inside of the adjacent polygon. This tool will not work when attempting to digitize a polygon inside of another polygon (use the Split tool to do that). The scale restriction and MMU also apply to this tool. If several polygons are created with a single line and some are below the MMU, a warning message will appear. If "No" is selected on the warning message only the polygons that fall below the MMU will be removed.

Use this tool to digitize a line. Once the line is complete, a message box will allow the classification to be set as outlined below.

Use this tool to split a line. The original line will retain its attributes and the message box will allow the classification to be set as outlined below.

Use this tool to digitize a line. Once the point is digitized, a message box will allow the classification to be set as outlined below. If there are many points to be digitized with the same attributes, it might be easier to add them using the standard ArcView Draw Point tool and attribute them all at once later

Once polygons are completed using the Add and Append tools, a dialog will appear to guide assignment of classification attributes.

The "Field List" displays the hierarchical structure of the fields in the scheme. "Current Attribute Selection" shows the classification type, if any, currently selected. Either select "Use Current Selection" or select a new classification type by clicking through the desired classification attributes in the "Select New Attributes" window. As new attributes are selected they will be displayed in the "New Attribute Selection" window. The "Use New Selection" button will be activated when the attribute in the lowest hierarchical level for the new classification is selected. To change the selected attribute at the same hierarchical level in the "New..." window, select another attribute in the "Select..." window. To select a different attribute at a higher level, select the level in the "New..." window.

This tool splits one or more polygons into several polygons. All of the attribute information for the resulting polygons will be the same as the original(s) but can be changed as explained below under "Tools from the Right Mouse Button". Please note that due to a bug in ArcView, this tool sporadically works when attempting to split along the inside border of a donut polygon. The scale restriction and MMU also apply to this tool. If several polygons are split and some of the resulting polygons fall below the MMU, choosing "No" will remove the entire line and merge the split polygons back together.

This button will place a MMU sized red box on the view by clicking the button and then clicking the View at the desired location. This box allows users to estimate the size of features in the imagery relative to the MMU. This box will disappear when panning, moving from the current extent by zooming in or out, or after completing a polygon. To use this feature while adding a new polygon see "Tools from the Right Mouse Button" below.

This button brings up a dialog to display the cursor's x/y position in the upper right hand corner of the ArcView window in either the coordinate system of the view (default) showing from 1-5 significant digits, or in degrees, minutes, and seconds. This requires that the view's projection be set and the map units specified.

This button will read through the attribute table and attempt to fix any mismatches between the UniqueID and attributes. This will be necessary if the "Automatic" method of assigning UniqueIDs was used on an existing classification scheme. The attributes for each record will be read and the UniqueID will be changed. The features with attributes that do not have a corresponding UniqueID will be listed at the end of the process by record numbers. These features will also be selected in the theme. If the shapefile does not have a field showing the record number, this can be added easily. Open the attribute table, begin editing it, and add a numeric field. Use the Calculate button and type in rec (without quotes) in the text input area of the dialog box.

Tools from the Right Mouse Button

Click and hold down the right mouse button to view a list of additional tools and options:

"Panning" will recenter the display over the spot where the right mouse button was clicked. This is useful while digitizing large polygons that don't fit entirely within the view frame.
"Pan to location" will recenter the display at a user selected position. This tool brings up a message box that allows the user to put in a specific coordinate location in map units.
"Show attributes" will display a message box showing the habitat attributes for the currently selected polygon.
"Change habitat attribute" will allow the user to change the habitat attributes for existing polygons that are selected.
"MMU Box" places an MMU box on the View where the right mouse button was clicked (can be added while digitizing a polygon).
"Polygon Area" shows the area of a selected polygon.