Thematic Maps and the Dot Method
To show where children are sitting in the school ground we put one dot for each place on paper. In the same way dots on a map show where and how many things are spread in a region.
A map that shows information on one special subject is a thematic map. A distributional map shows how something is spread over a region. In the dot method, dots are used for data obtained by counting.
Key idea 1 : What is a distributional map? — An ordinary map shows places. A distributional map shows how a thing like rainfall, people or cattle is spread. Its figures are needed to draw it. There are three methods: dots, shades and isolines.
Key idea 2 : Deciding the value of a dot — First the value of one dot is fixed, e.g. one dot = 1000 trees. For this the lowest and highest figures of the region are checked. Then the number of dots for each unit is worked out. The size of the dots is always kept equal.
Key idea 3 : Where to place the dots — While placing dots, land form, water sources, roads and railways are considered. Rural people are shown by dots and urban people by circles. The method suits best a thing that is freely scattered over the region.
- Easy : A taluka has 24,000 goats and 1 dot = 4,000 goats. How many dots? — 6.
- Medium : If 1 dot = 500 trees, dots for 3,500 trees? — 7.
- Exam-type : Dot method is for which data? — Data got by counting.
In the figure: Three methods of distributional maps.
Dot = counted number; equal size, fixed value.
Dots are not put anywhere at will; land form, water and roads are considered.
Memory clue: Dots = counting. Memory clue: "Count and dot".
Spot the difference
| Point | Rural | Urban |
|---|---|---|
| Symbol | Dot | Circle |
| Population | Shown by dots | Shown by circles |
Practice questions
- 1What is a thematic map?
- 2Which are the three methods of showing distribution?
- 3How should the size of a dot be in the dot method?
- 4If 1 dot = 800 cows, how many dots for 4,800 cows?
- 5What is considered when deciding where to put dots?
- 6How are rural and urban people shown on a map?
- 7For what kind of thing is the dot method most suitable?
- 8Which method will you use to show schools of your district and why?
Show answers (try them yourself first)
- 1A map showing information on a special subject.
- 2Dots, shades and isolines.
- 3Equal.
- 46 dots.
- 5Land form, water sources, roads and railways.
- 6Rural by dots, urban by circles.
- 7A thing freely scattered over the region.
- 8Dot method, because schools can be counted and are scattered.
Choropleth Method
If in a results chart a class with high marks gets a dark colour and one with low marks a light colour, we see at once which class is ahead. On a map shades of colour do the same work.
In the choropleth method each sub-administrative unit (e.g. a taluka) gets only one value and a shade according to the class of that value. Higher value means darker shade.
Key idea 1 : Data and classes — Data from measurement or surveys is used. Looking at the smallest and largest values, 5 to 7 classes are made, e.g. literacy groups of 40–50%, 50–60%.
Key idea 2 : How to give shades — Each class gets a shade of one colour or a black and white pattern. As the value rises the shade or pattern becomes darker. A key (table of classes) must be given beside the map.
Key idea 3 : One value for one unit — This map does not show where inside a taluka it is high or low. The whole taluka is coloured in one shade. So the method suits averages like density or literacy rate.
- Easy : If the lowest literacy is 42% and highest 90%, how many classes? — 5 to 7.
- Medium : Taluka 1 has 85%, taluka 2 has 55%. Darker shade to? — Taluka 1.
- Exam-type : How many values to one taluka? — Only one.
In the figure: Steps of a choropleth map.
One unit = one value = one shade; more = darker.
A choropleth map does not show a separate value for each spot in a unit; only the one value of the unit.
Memory clue: More = darker. Memory clue: "Dark means dense".
Spot the difference
| Item | Dot method | Choropleth |
|---|---|---|
| Symbol | Dot | Shade of colour |
| Value | Counted number | One value per unit |
| Example | Number of animals | Density of population |
Practice questions
- 1To which unit is one value given in the choropleth method?
- 2How many classes are made for a choropleth map?
- 3What happens to the shade as the value rises?
- 4When are black and white patterns used in a choropleth map?
- 5Why give a key of shades beside the map?
- 6State the difference between choropleth and dot methods.
- 7Why is a choropleth map suitable for showing density?
- 8Choose a method to show talukawise literacy rate of a district and give a reason.
Show answers (try them yourself first)
- 1To a sub-administrative unit (e.g. taluka).
- 25 to 7.
- 3It becomes darker.
- 4When colours cannot be used.
- 5To know which shade is of which class.
- 6Dots = counted numbers; shades = one value per unit.
- 7Because density is an average value of the unit.
- 8Choropleth, because each taluka has one value.
Isopleth Method
You have seen lines on a hill map joining places of the same height. Weather maps too have lines joining places of equal air pressure. Such lines can be called isolines.
Showing the spread of a thing that changes continuously over a region (e.g. height, temperature, rainfall) by lines joining places of equal value is the isopleth method.
Key idea 1 : Point-related data — Units like taluka or district are not considered here. The data belongs to a particular spot (point). The value is written at that spot on the map. The more spots we have, the more accurate the map.
Key idea 2 : How lines are drawn — Looking at the lowest and highest values the gap between lines (interval) is fixed, e.g. one line for every 100 mm rain. Places of equal value are then joined by a line. The change between two places is assumed to be even.
Key idea 3 : Reading the map — If lines are close together the change is steep and if far apart the change is gentle. The map shows the natural trend of the thing, i.e. where it rises and falls.
- Easy : Rain lines of 100, 200, 300 mm are close. Change? — Steep.
- Medium : Lines are far apart; the change is? — Gentle.
- Exam-type : Which method for temperature? — Isopleth.
In the figure: How an isopleth map is drawn.
Continuous = isolines; close = steep, far = gentle.
Isolines do not follow taluka boundaries; they join places of equal value.
Memory clue: Close = steep, far = gentle. Memory clue: "Close means strong".
Spot the difference
| Thing | How it changes | Method |
|---|---|---|
| Height, temperature, rainfall | Continuous | Isopleth |
| Animals | Scattered | Dot |
| Density (by taluka) | One value per unit | Choropleth |
Practice questions
- 1For what kind of things is the isopleth method used?
- 2What is point-related data?
- 3How is the interval between lines fixed?
- 4What do we understand if the lines are close?
- 5What do we understand if the lines are far apart?
- 6What is the benefit if data of more places is available in an isopleth map?
- 7State the difference between choropleth and isopleth methods.
- 8Choose a method to show temperature distribution in Maharashtra and give reasons.
Show answers (try them yourself first)
- 1Continuous ones: height, temperature, rainfall.
- 2Data belonging to a particular spot.
- 3By looking at the lowest and highest values.
- 4The change is steep.
- 5The change is gentle.
- 6The map becomes more accurate.
- 7Shades = one value per unit; isolines = point values and lines.
- 8Isopleth, because temperature changes continuously.
Geographical Field Visit
Reading about a river in a book is very different from standing on its bank. Seeing a place directly helps us understand and remember better.
Going to a place to experience geographical concepts and elements directly is a field visit. It helps to understand the relation between man and environment.
Key idea 1 : Preparation — Fix the place and purpose. Decide what to observe. Study the location map and route map. Plan distance, transport and time. Prepare a questionnaire with teachers. Take a permission letter if needed.
Key idea 2 : What to carry and precautions — Notebook, questionnaire, pen, pencil, scale, tape, compass, bag for samples, maps, camera, first-aid box. Obey teachers, do not go alone to unknown far places, talk to local people and do not harm the environment.
Key idea 3 : Report writing — After the visit a report is written from the data. It has introduction, location and route map, physiography, climate, population, environmental problems and measures, land use and conclusions. Add photographs where needed.
- Easy : Where can a visit be? — River bank, dam, village, forest, museum.
- Medium : Which maps before the visit? — Location and route map.
- Exam-type : What is at the end of the report? — Conclusions.
In the figure: Field visit: from preparation to report.
First preparation, then observation, care and finally the report.
A field visit is not just a picnic; it has a purpose, questionnaire and report.
Memory clue: Prepare → observe → care → report. Memory clue: "Plan, look, protect, write".
Spot the difference
| Picnic | Field visit | Difference |
|---|---|---|
| Aim is fun | Aim is study | Purpose |
| No report | Report is written | Records |
Practice questions
- 1What is a field visit?
- 2How to prepare for a field visit?
- 3Which things should be taken on a field visit?
- 4Why talk to local people during the visit?
- 5State any three precautions during the visit.
- 6State the points in a field visit report.
- 7Why keep a first-aid box with us?
- 8If you visit a place in your village, what will you prepare?
Show answers (try them yourself first)
- 1Studying geography by going to the actual place.
- 2By fixing place, purpose, maps, route, time and questionnaire.
- 3Notebook, pen, tape, compass, maps, camera etc.
- 4To understand local conditions.
- 5Obey instructions, do not go alone, do not harm the environment.
- 6Introduction, maps, physiography, climate, population, land use, conclusions.
- 7To help in an emergency.
- 8Place, purpose, maps, questionnaire, material and permission.