A SIMPLE METHOD FOR CODING GEOGRAPHICAL LOCATIONS IN A POST‐COORDINATE INDEX

Place names are a problem in co‐ordinate indexing, in that they exist in very large numbers, whilst individual names may be used only infrequently. To counteract this inflow of features, and a corresponding increase in feature cards, Jolley has suggested a method which employs subcodes or polygraphs. This system enables a place name to be represented by a random combination of alphabetical letters or numerals. The combinations may consist of two or more characters. In this way Manchester could be expressed as A+B or A+B+C or any other random arrangement. If one alphabet is used, two‐letter combinations (digraphs) will permit 325 names to be accommodated whilst three‐letter combinations (trigraphs) will accommodate 2,600. The system is simple to apply, but a supplementary index has to be constructed to connect names with codes.