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The build area tool is used to create an area entity from polylines that already exist on the map. In high volume map production it is often faster to draw all the boundary lines on a particular layer as simple polylines and then come back in a second pass using this tool turning them into areas. To draw area boundaries from scratch use the Draw Area button.
Assumptions:
•The build area tool only works with polylines.
•All polylines must have their end points connected to any other polylines around the perimeter of the area. If this may not be the case, then first run Break polylines at intersections found on the Advanced Tools menu.
To build an area from existing geometry
1) Specify a Current Layer (The layer to contain the final polygon area.) and Current Feature (The Feature Name to be used for the area entity.) on the edit tool bar. If necessary first use the New Feature Button to create the feature to be drawn. The current layer must also be the layer that contains the existing polylines that will be used to fabricate the area.
2) IMPORTANT: Make sure there is a fill color assigned to the current layer in order to see the results.
2) Click the  button on the Editing Toolbar (or Ctrl-Shift-M).
3) Using the mouse, move the cross hairs to any point inside the area being created, and then press and release the left mouse button.
4) If the area is successfully built, it will immediately be filled in. If the area does not fill then a gap or other bad geometry was encountered while trying to connect the polylines forming the border of the area. Small X's will be placed at any polyline endpoints where the problem might be. If there is no fill color assigned to this layer it could be that the area was successfully built but cannot be seen, because it is not filled in.
Quick Reference:
Left Click Pick interior point
Middle Click Update current feature
S Highlight vertexes
Ctrl-S Highlight vertexes and keep them on
Shift Hold down to disable snaps
Notes:
•After the area entity is created the polyline entity(s) it was made from still exist. In most applications it is good practice to go back and delete the original entities after all the areas have been created. To do this use the delete entity tool with the entity filter option set to polylines only.
•The build area tool also recognizes closed polylines as islands inside the area and automatically excludes them by creating holes in the main area entity. Any polylines that do not form closed loops are ignored.
•See also the Convert Polylines to Areas tool for use on special layers.
•Tool use instructions will also appear in the footer of the Think GIS window in the Instructional Bar.
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