How To Display Selected Contour Data

If you have been using the contour data from 2002 Ortophoto Project, you know that the data is very dense and you may want to display only certain contour values instead of all the data.

Here is a tip on doing this in ArcGIS:

After you have loaded the contour layer or layers, cont_02_200 & cont_02_400, open the Properties for the layer by right-clicking on the layer name in the table of contents. Click on the Definition Query tab.

Users on the County network including VPN with contour data from ArcSDE:

cast(elevation as int) % 100 = 0

This will display only those contours with an elevation that is a multiple of 100. The percent sign is called the modulus operator and is used to perform the division. The cast command converts the floating point elevation field to an integer. Of course, you can change 100 to any other number you want.

Non-county users with contour data in Shapefile format:

"ELEVATION" / 100 in (1,2,3,4,5,6,7,8,9,10)

Shapefile users will have to use this somewhat cumbersome workaround since the modulus operator does not seem to be supported for Shapefiles. This statement divides the elevation value by 100 and looks for results equal to 1 - 10. These correspond to elevation values of 100, 200, 300, …, 1000. Since you have to list out all the values, this technique is best suited for small areas where the range of elevation values is small. Naturally, you can change 100 to any other number and make the list as long or short as you want.

ArcView 3.x users

"ELEVATION" MOD 100 = 0

I didn't actually try this, but it should work. The modulus operator is available in ArcView 3.x so you should be able to find it in the Help.