The aim of this book and the rationale behind writing it are twofold, and are born of experience in working in the field with geologists, builders, land­ scapers, and people in the construction and building trades in general. This author, in his capacity as a geologist, air photo interpreter, and surveyor, has been asked to consult on very simple tasks that should be a part of the general knowledge of nearly everyone in the building trades. There is a definite and clear need for a short, simple, well-illustrated, and concise book that treats problems encountered every day by people in the field, and for training such people. This is such a book. The primary aim of the book, then, is not to write about new knowledge in the areas of photogrammetry or mathematics, or to discuss the latest procedures in using complex electrooptical surveying devices, but to give the common, everyday worker in the field (and there are many of them) some assistance and guidance.