Note: The procedure below is for ArcGIS 9.3.1 or earlier versions. Starting at ArcGIS 10.0, expressions in the Calculator are created using only VBScript or a standard Python format.
Contour maps typically symbolize index contours with a thicker line symbol. This article shows how to do this with data that only has contour height in the attribute table.
Code: dim dIndexInterval as double dIndexInterval = 50 ' set to interval of index contours ' in z units (typically 5 times ' regular contour interval' dim dCont as double dCont = [Contour] ' Set to contour height field dim i as long i = dCont / dIndexInterval if ( ( dCont / dindexInterval) - i = 0) then dim j as long j = 1 ' is an index contour else j = 0 ' is not end if