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How To: Create a buffer zone around selected features

Summary

You may want to create a new theme which includes only those features that exist within a particular spatial area or that have certain attribute values. These features may be selected with any AutoCAD selection tools or ArcCAD tools (e.g., RESELECT, ASELECT, NSELECT). The entities and features do not have to be visible on the screen for the features to be selected, but entity-feature links must be present.

Once you have selected the desired features, you can use EXTRACT to create a new theme of only the selected features. This new theme will be the input theme for the BUFFER operation, which generates buffer zones around input theme features. The PAT of the output theme will have an additional item called INSIDE. The value for each record will be either 100 (area inside the buffer zone) or 1 (area outside the buffer zone).

Procedure

The following is an example of creating a buffer around roads:

  1. Create a feature selection set from an ArcCAD theme.

    Code:
    Command: RESELECT
    Theme name (?/<default>): ROADS
    Reselect by?(Circle/ENtity/Expression/Polygon/Window): E
    Logical expression: ROAD_CODE = 'PRIMARY'
    Roads arcs: 7 of 14 selected

  2. Create a new theme which includes only the selected features.

    Code:
    Command: EXTRACT
    Input theme (?/<defaults>): ROADS
    Output theme (?): PRIMROAD
    Theme PRIMROAD is not defined.
    Defining PRIMROAD...
    GIS data set <PRIMROAD>: <CR>
    Symbol number (1-100) <0>: <CR>
    Extracting features from roads to create primroad
    Extracting...

  3. Create polygon themes by generating buffer zones around input theme features.

    Code:
    Command: BUFFER
    Input theme (?/<default>): PRIMROAD
    Output theme (?): ROADBUF
    Theme ROADBUF is not defined.
    Defining ROADBUF...
    GIS data set (?/<default>):
    Shade symbol number (1-100) (?/<0>):
    Buffer using? (Item/<Constant>): <cr>
    Buffer distance: 200
    Fuzzy tolerance <compute>: <cr>