The cities of the world will probably at least double in size before the end of the century, due to world population increases and the apparently irreversible trend from country to city living. The success of the vast building program that this increase will necessitate will depend, ultimately, upon adequate knowledge of the subsurface conditions of all the ground that will be covered by this urban expansion.

Coordination of existing records with the results of new investigations and facts revealed by all new excavation is essential for every urban area. This can be done only in close association with local geology. Engineering-geological maps provide the best means of recording this vital information. Some cities have made a good start at the preparation of such maps; examples are given. All cities must have such maps as basic tools for all future planning if inevitable expansion is to be saved from costly errors. Broad guidelines for this essential public service are presented.

This paper is a summary of my oral presentation at the 1972 Annual Meeting of The Geological Society of America held in Minneapolis, and is based on material in Cities and Geology (Legget, 1973), which was in press at the time of the meeting.

The current rate of growth of the cities of North America is little short of phenomenal, as a glance at the Twin Cities area will clearly show. This rapid expansion is a reflection of the increase in population growth since the end of the second world war, assisted to a degree by the corresponding increase in the standard of living. It is but a beginning of a growth pattern that will probably see urban development throughout the world doubled by the year 2000.