Soundex

Soundex technology was originally developed by US Government agencies to help with the cataloging of census and immigration details.

A site at NARA gives full details.

Names or text values are reduced to a four-character code based on how it sounds. Thus, similar names such as Millar and Miller have the same code of M460. Incidentally, so do the various European alternatives of Moeller, Mohlert, Mueller and Muller!

Daisy has a mapping format, Soundex, specifically for this type of analysis.