Obtaining length of non projected feature (gcs_wgs_84) in meters instead of decimal degrees?

Question

I could not find a post which answered to my problem and I hope I didn't miss it, in case I did I apologize.

I'm working with Arcgis 10 and I have a multiple lines feature with gcs_wgs_1984 geographic coordinate system (same of the data frame).

I'm not very familiar with coordinate systems and projections and I've being stuck with this problem for a while, so I hope you can help.

I want to see in the attribute table of the feature the length of each line, but it is obviously shown in decimal degrees.

Which is the best solution to get that length in meters? Should I project my feature in a projected coordinate system? Which system would suit me better for this porpose? If I project a feature in a projected coordinate system will it still appear on the non projected data frame?

I tried to project it (project tool) in wgs84 Utm 32N but it gives me unknown error 999998.

The zone I'm working on is the city of Milan in Italy, if that's of any use.

Answer 1

With 10.2.1 and above, you can use the Add Geometry Attributes tool to add a field with the length of the features. The tool lets you specify the coordinate system you want to use, in case it is different from the dataset's system.

With 10.0, you should work in ArcMap:

• set the coordinate system of the data frame to WGS 1984 UTM 32N
• add a field to your feature class (choose double as format)
• open the attribute table, right-click the new field and choose Calculate Geometry
• choose 'Length' as property to calculate, and check the option to use the data frame's coordinate system.

This is enough because the coordinate system of the input and output have the same datum (WGS 1984). If they had a different datum, you would need to project the data before the calculation, to specify a datum transformation.