#### SUMMER 2003GEOHAZARDS COURSE AT UWI, MONA - page 036

Prepared and compiled by Rafi Ahmad, Unit for Disaster Studies,
Department of Geography and Geology,
University of the West Indies, Mona, Kingston 7, Jamaica

Compass bearings
A bearing is the compass direction from one point to another. It is expressed in degrees west or east of true north (quadrant bearing), or in degree from 0 to 360 (azimuth bearing). This concept will be explained both in Lab. and field sessions.

Scale
Topographic maps model the surface of the Earth. A scale establishes the ratio by which all real dimensions must be multiplied to determine the corresponding dimensions of the model. In case of topographic maps, the scale factor is a fractional multiplier, such as the widely used ratio scale of 1:50,000. This can also be expressed as a fraction (1/50,000 X), indicating that the portion of the Earth represented has been reduced to 1/50,000 of the actual size.
A fractional scale 1/50,000 (1:50,000) means that one unit (e.g., m, cm, foot) on the map represents 50,000 of the same units (m, cm, foot) on the Earth's surface.
A verbal scale is used to simplify the fractional scale. For example, because there are 100 cm in a m, the ratio scale 1:50,000 (one cm on the map equals 50,000 cm on the ground) may be expressed as a verbal scale of "one cm equals 500 m".
A graphic scale (or bar scale) is always printed in the lower margin of the topographic map.
See the topographic maps.
Scale constraints on use of maps.
Map Symbols and Marginal Information
Explained with the help of topographic maps.

Contour lines
Topographic maps are scaled - down models of the Earth's 3 - dimensional surface, represented on 2 - dimensional medium. In section 8 the length and width aspects and their transfer from real world to the map were explained. The third dimension, height (or elevation), is shown using contour lines, or simply elevation contours. A contour line connects all points on the map having the same elevation above sea level (A.S.L. or M.S.L.).
The contour interval is the vertical difference in elevation between adjacent contour lines and is indicated on the map. Some of the contours, called index contours, are drawn prominent with their values written on. On some of the Jamaican topographic maps the contour intervals are not uniform. Before using these maps it is wise to always check the contour interval. Rules for contour lines are explained separately.

Relief
Relief is defined as the difference in elevation between any two locations on the map.
Total relief and local relief.
Contour patterns and landforms.
Benchmarks, Trig. Points and spot heights.
Measurement of linear distances and area on the topographic maps
Explained on a separate sheet.
Topographic profile
Explained on a separate sheet.
USE OF GEOLOGICAL MAPS
Study Kingston Geological Sheet No. 25 and extract geologic and structural information relevant to the study area. Insert this data on the 1:10,000 sheet.
Description of rocks will be explained in the field.
Engineering properties of rocks through a flowsheet.