ISOPLETH

The term isopleth has been derived from greek word isos meaning same and  plethron meaning measure . Thus isopleths are lines joining places of equal value.This value may be in the form of quantity, intensity or density

 Following are few examples of isopleths

Isobar :equal pressure .

Isotherms:equal temperature

Isohyet -equal rainfall

Isohaline :equal salinity

Sometimes, the space between isospleths are shaded or coloured whose intensity increases with the increase in value .this bring in more clarity of distribution.

Isopleth are used to show the following :

-climatic elements

-temperature

-pressure

-cloudiness

 While showing density of population and distribution of crops etc. care should be taken to show the index of concentration before actually plotting them on the map.

 

Merits

1. Isopleth are more scientific than other methods of showing distribution and effectively show the distribution and variations.
2. This is especially useful for climatic maps such as isobars, isotherms , isohyet etc.and is known as the main tool for the meteorologists
3. It is very easy to determine the gradient  (rate of change )with the help of isopleth maps.
4. When isopleth are wide apart ,they show low gradient but when they are closer  together they show high gradient .
5. Isopleth lines are independent of political boundaries and best suitet to show the natural pattern of distribution of an element .
6. isopleth is the most suited method for showing elements having transitional values ,this is a reason that isopleth are invariably used to show the distribution of temperature ,pressure and other climatic elements .

Demerits

     1.The drawing of isotherm often needs interpolation ,which is a difficult process.

    2.The method often suffers from lack of sufficient data.

 

choropleth method

CHOROPLETH METHOD

The very word choropleth has been derived from the two greek words namely “choros” meaning “place and “plethron” meaning “measure”. Thus  the literal meaning of choropleth is quality in area . This method is primarily used to show the distribution of commodities per unit area, average measure or percentage etc.

Example density of population, male-female(sex)ratio ,percentage of agricultural land to the total land or percentage of hindi speaking population to the total population  etc.

     METHODS OF CONSTRUCTION

•      Obtain an outline map of the concern area along with the administrative boundaries.
•       Arrange the data in ascending or descending order.
•       Divide the given data in proper class intervals and name them A,B,C,D,E etc .and using a pencil write  A,B,C,D,E on the map according to data of the concerned  administrative unit
•  Fix suitable shades for these class intervals and place them in their respective administrative units.
•   Care should be taken while selecting the shades that the intensity of shades increases with        increase in value shown.
• Make the index and show all the shades corrrectly along with their class intervals in proper sequential order
•        Write the heading appropriate to the size and data given on the map

OTHER BLOG

http://www.crpfgeography.blogspot.com/

DOT METHOD

Dot method

It is the most important, useful and simple method of showing the distribution on the map. This method is particularly useful for showing absolute figures. Dots are put on the map to show the concerned distribution. Each dot is assigned a special value. The dots are put according to the actual distribution of the element to be shown. This method is used to show the distribution of population, livestocks, agricultural production of a certain crop, production of minerals etc                          

CONSTRUCTION

Construction of dot map is not an easy as it appears to be

·        It requires  some- preliminaries which need the following

·        Outline map of the concerned area with administrative division. The smaller the division, the more accurate will be the map. Absolute figure of element to be shown. These figures should be according to the administration divisions shown on the map.

·         Relief map, drainage map, climatic map(temp, rainfall)

SPACING OR PLACING OF DOTS

The third step after the value and size of the dot is the placing of dot on the map. As a rule the dots are placed exactly according to the actual distribution of the concerned element.

No dots are placed over negative areas i.e. area having no distribution. rugged, infertile, densely forested area, mashes, water bodies are some examples of negative areas .the negative areas are marked lightly with a pencil and erased with eraser after placing the dots

       

 MERITS

Ø      This method is better than any other method of showing distribution because of its accuracy

Ø      The distribution of dots is similar to the commodity shown by them.

Ø      This is the best method for showing the absolute figures.

Ø      It provides a better visual effect and is more useful than the other methods of showing distribution.

Ø      We can have an idea of the figure shown on the map by counting the dots.

Ø      A dot can be converted into choropleth or isopleth  but these maps can’t be transferred into a dot map.

Ø      We do not have to look at index, time and again as in case of choropleth maps. The dot maps can be easily read

Ø      More than one element can be shown on a single map by using multiple dot map method.

DEMERITS

Ø      It requires a good deal of practice to draw it.

Ø      This is useful for absolute figure only. Relative figure such as density of population proportion of scheduled caste population to the total population, proportion of cultivated land to the total land etc can’t be shown by dot method.

Ø      The dot method looses much significance if the data is not available for small division of areas.

             It is almost impossible to draw a perfect dot map in the absence of complete

            geographical knowledge of the area and knowledge of the element to be shown