Index was outside the bounds of the array error in the Thiessen polygon creator tool or Loadbuilder

  Applies To 
  Product(s): Bentley WaterCAD, Bentley WaterGEMS
  Environment:  N/A
  Area:  Calculations
  Original Author: Mark Pachlhofer, Bentley Technical Support Group

Problem Description

When I try to use a particular shapefile in the Thiessen Polygon Creator tool or in Loadbuilder I get an 'Index Out Of Range Exception' error that says: " Index was outside the bounds of the array." Why is this?

Reason 1 (Version and Earlier)

This message is usually due to the fact that the shapefile is a ZM, Z, or M shapefile. This indicates that the shapefile has 3 dimensions instead of the normal 2 dimesions of a regular shapefile. The 3rd dimension being height or elevation, hence the ZM, Z, or M.  


Download the latest version of the WaterCAD or WaterGEMS software

Click here for download instructions

This issue was resolved in a patch set for version, so downloading this version or a newer version elminates the issue. 

Or you have the option of speaking to your GIS professional and have them remove the ZM, Z, or M from your shapefile

Reason 2 (Not Version Specific)

The Shapefile format (SHP) requires at least three files in the same directory, with the same name and the following extensions

File Extension



Shape Format: Describe the feature geometry such as points, polylines, and polygons


Shape Index Format: A positional index of the feature geometry to allow seeking forwards and backwards quickly


Attribute Format: Columnar attributes for each shape, in dBase III format

In addition to the three mandatory files listed above, you can include the following optional files:

File Extension



 Project Format; contains the coordinate system and projection information, a plain text file describing the projection using well-known text format

.sbn and .sbx

 A spatial index of the features

.fbn and .fbx

 A spatial index of the features for shapefiles that are read-only

.ain and .aih

 An attribute index of the active fields in a table or a theme's attribute table


 A geocoding index for read-write shapefiles


 A geocoding index for read-write shapefiles (ODB format)


 An attribute index for the .dbf file in the form of shapefile.columnname.atx (ArcGIS 8 and later)


 Metadata in XML format


 Used to specify the code page (only for .dbf) for identifying the character encoding that will be used


Make sure that the folder containing the SHP file also contains the associated SHX and DBF files with the identical file names.