THIESSEN first requires you to specify if the points
for polygon construction are in a vector file or an image file, and to
input the name of that file.
The identifiers for the points are integer numbers, with each point assigned a different identifier. This is so the output image will code each cell with the identifier of the point to which it belongs. Thiessen polygons are formed by the regions of common identity.
Then, THIESSEN requires you to input a name and title
for the output image. If a vector file is used for point input, specify
the desired file type and data type of the resulting image. The default
file type is ASCII and the default data type is integer. It then displays
the minimum and maximum X and Y coordinates and requires you to enter the
number of rows and columns to span the region.