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You can create a grid file (and hence map) with data only inside a particular outline (ie. building, lake boundary, mine boundary, etc) by saving the boundary outline to a BLN file (BLN flag=0) and then either using the BLN file as a blanking file, using it as a fault file when gridding, or using it as a breakline file and then a blanking file.

1.     Blank outside the outline.
Create a BLN boundary file defining the boundary you want the data limited to, and blank the grid file outside the boundaries defined in the BLN file.

a.     Go to Grid | Data, select your data file and click Open. Grid your data using your regular gridding method (it will create the rectangular grid).

b.    Go to Grid | Blank.

c.     Select the grid file and click Open.

d.    Select the BLN file and click Open.

e.     Enter a name to save the new grid file as and click Save.

f.     Create the map from this new blanked grid file.

2.     Use a fault file to define your outline.
Create a BLN boundary file that defines the outline you want and use the BLN file as a fault file during gridding.

a.     Go to Grid | Data, select your data file and click Open. 

b.    In the Grid Data dialog box, select a gridding method that supports faults. Only some gridding methods support faults (Inverse Distance to a Power, Minimum Curvature, Nearest Neighbor, and Data Metrics). Kriging does not support faults, but Minimum Curvature creates a result that is very similar to Kriging.

c.     Click on the Advanced Options button.

d.    Go to the Breaklines and Faults tab.

e.     Specify the BLN as the fault file.

f.     Click OK and OK to create the grid file.

g.    Create the map from this grid file.

3.     Use a breakline file and also blank the grid.
This is most useful when trying to create bathymetry contours for a lake or other closed area. Create a BLN boundary file defining the outline of your data limits (ie. the lake edge), including a third column of Z values in the BLN file for the breakline (for a lake, this could be 0 for the lake edge).

a.     Go to Grid | Data, select your data file and click Open.

b.    In the Grid Data dialog box, select the Kriging gridding method.

c.     Click the Advanced Options button.

d.    Go to the Breaklines tab.

e.     Specify the BLN file as a breakline file.

f.     Click OK and OK to create the grid file.

g.    Go to Grid | Blank.

h.     Select the grid file and click Open.

i.      Select the BLN file and click Open.

j.      Enter a name to save the new grid file as and click Save.

k.     Create the map form this new blanked grid file.

You might want to create the BLN file and try each of the above methods to see which results best suit your needs.

See Also:

How can I create a BLN file?

How can I grid only the area inside my data limits?

How can I calculate the volume and/or area inside an irregular polygon?