Page 13 - 6589

PRACTICAL WORK №2
READING TOPOGRAPHIC QUADRANGLE MAPS

PURPOSE

The objective of this work is to determine coordinates of points on the map.
It will be the most accurate information containing the geographical location of
any place.

LOCATING THE MAP ON THE EARTH - LONGITUDE AND
LATITUDE
The first important question a user of a map must answer is: "What part of
the Earth's surface is portrayed?" In order to answer this question, one must be

able to specify location on the surface of the Earth. The location of points or areas
on the surface of the Earth can be shown by means of two groups of intersecting
circles known as latitude and longitude (Figure 2.1). Both latitude and longitude
lines represent subdivisions of a circle and are therefore measured in degrees,

minutes, and seconds. Remember that there are 60 minutes in a degree and 60
seconds in a minute.
Latitude lines are lines that encircle the Earth in east-west-parallel planes
perpendicular to the Earth’s axis (Figure 2.1). Latitude increases in either the

north or south direction moving away from the zero degree line around the middle
of the Earth (the Equator). Thus, latitude lines increase in value north and south
from 0° at the Equator to 90° at the Earth’s poles.
Longitude lines are lines that encircle the Earth from pole to pole in north-

south-parallel planes parallel to the Earth’s axis. Longitude increases in either the
east or west direction away from the zero degree line called the Prime Meridian.
Because there is no natural ‘middle’ to the Earth in a vertical-, axis-parallel
orientation, the Prime Meridian is defined as the N-S circle that passes through

the town of Greenwich, England (the reason for this is historical: Greenwich was
the site of the British Royal Observatory and of the telescope used to make the
astronomical observations on which the longitude system was originally based).
Longitude lines increase in value from 0° at the Prime Meridian to 180° at the

International Date Line.

11