To determine the size of the continent, ocean, river or other geographical object, it is necessary to learn previously its extent in degrees. The system of geographical coordinates allows to define unambiguously the provision of any point in space, and, having the card before eyes, you can always find extreme points of an object and determine extent in degrees.

## It is required to you

- - map in an electronic or paper look, with the indication of parallels and meridians.

## Instruction

1. If you need to find object extent from the South on the North (or from the North on the South), define whether there is it entirely in one hemisphere. Look, on the center of the globe there passes the imagined line – the equator, an object it either crosses, or is not present. Depending on it it is necessary to determine extent differently.

2. Find the width of the most extreme points of an object. If it is necessary to determine extent by any meridian, at first define the extreme points, for example, the continent lying on this meridian.

3. To learn on what parallel the point lies, find horizontal lines on the card, at the left and on the right coordinates of these lines, as a rule, are specified (for example, 30 ⁰). Mentally draw a parallel horizontal line and approximately define to what parallel it will correspond.

4. If before you the electronic card, guide the cursor at a point and use the result received automatically. Consider that coordinates are designated in degrees, minutes and seconds (in one minute 60 seconds, and in one degree – 60 minutes). Sometimes instead of minutes or seconds it is possible to meet designations of the tenth shares – in that case will easier make calculation.

5. Having learned the width of two extreme points, find a difference between them. If both points lie in one hemisphere (southern or northern), just subtract smaller from bigger value. Subtract the values expressed in degrees and minutes just as hours and minutes, and decimal fractions it is possible to subtract even by means of the calculator.

6. If points lie in different hemispheres, on the contrary, put values of coordinates. For example, if the northern point lies on a parallel 20⁰45', and southern 12⁰30', the total length of an object will be equal to 33⁰15'.

7. Or from the West on the East count object extent from the East on the West similarly, only not on width, and on longitude. Learn on what meridian extreme points lie and subtract from bigger value smaller (if an object is entirely located in one hemisphere – western or east).

8. In case an object crosses a zero meridian instead of subtracting the longitude of points, put them among themselves. A certain complexity is represented by search of extent of the object crossing a meridian 180 ⁰, for this purpose subtract the longitude of both points from 180 ⁰ and put the received results among themselves.