B. Measurements

1. Orientation

Gravity is a fundamental element of surveying. Regardless the operation performed or instrumentation used, all surveying measurements are referenced to the direction of gravity. We can see gravity’s direction when we drop something or view a freely suspended plumb bob. Gravity’s direction defines a vertical line, Figure B-1. A horizontal line is perpendicular to a vertical line, Figure B-2.

Figure B-1 Vertical	Figure B-2 Horizontal

With few exceptions, surveying measurements are made in, or reduced to, horizontal and vertical orientations. Unless otherwise indicated, when interpreting measurements they are presumed to be in horizontal or vertical directions. For example, if a contemporary property description calls for “235 feet to an iron pipe”, the distance is taken as horizontal, Figure B-3, not along the ground.

Figure B-3 Horizontal Distance