Interpretation of maps - class-VIII

Cosmography is the science that deals with the general description and mapping of the universe, including the earth's place within it.

• Nathu La is a mountain pass in the Himalayas.
  
•  It connects the Indian state of Sikkim with China's Tibet autonomous Region.
  
•  In 1904, Major Francis Younghusband, serving as the British Commissioner to Tibet, led a successful mission through Nathu La to capture Lhasa.
  
•  Shipki La is a mountain pass and border post on the India-Tibet border.

 Most common map projections are based on three shapes.

Khyber Pass, Khyber also spelled Khaybar, or Khaibar is one of the important passes between Afghanistan and Pakistan. The pass connects Kabul with Peshawar. The pass has historically been the gateway for invasions of the Indian subcontinent from the northwest.

Sun always rises in the east. If you are facing the rising sun, you will be facing east. South lies to the right if one faces east. Therefore, to your right will be South.

Maps which are prepared with special themes are called Thematic maps. Distribution of temperature, rainfall, population etc. is shown on the map according to the date of different variables.

The main aim of maps is to show the location of a place and distribution of variables with distribution of people. Maps are useful to explain the variable of these variables in the region.

Variables like temperature, rainfall and polulation are known as special theme. Maps are useful to explain the distribution of these variables in the regions.

To draw distributional maps, we need statistical data of the variables. There are three ways to show distributional maps:

• Dot method
• Choropleth Method
• Isopleth Method

Distribution in maps is nothing but the distribution of variables like
temperature, rainfall and population which can be shown in maps. Distributions can be shown in the following ways:

• Dot Method
• Choropleth Method
• Isopleth Method

In these maps, the data regarding various geographical variables is
shown by shades or tints of various colours. While making such maps, the
data used for different variables is obtained through various
processes such as measurement, surveying etc.

A dot maps is prepared using statistical data. While preparing dot maps, only data gathered through counting is used. The way a variable is distributed throughout the region, the dots are used to show its distribution on the map.

In these maps, the data regarding various geographical variables is
shown by shades or tints of various colours. While making such maps, the
data used for different variables is obtained through various
processes.

The isopleth method is used to show the distribution of continuous variables (like temperature or rainfall) by connecting points of equal value with lines.

Distribution in maps is nothing but the distribution of variables like temperature, rainfall and population which can be shown in maps. Distributional maps are of three type:-

• Dot Method
• Choropleth Method
• Isopleth Method

To show distribution through dot method, we need to consider the size of the dot, the density of the variable and the scale of the map. The number of the dots to be given for the value of variable in each sub-administrative unit need to be decided first.

A dot maps is prepared using statistical data. While preparing dot maps,
only data gathered through counting is used. The way a variable is
distributed throughout the region, the dots are used to show its
distribution on the map.

Following precautions should be taken while using dot method for maps:-

• The size of a dot should be uniform.
• The distribution of physiography, water sources, transport system, etc.
  of a region should be considered while placing dots on a map.
• While showing population distribution, rural population is shown by dots and circles are used to show urban population.

A thematic map is a map that focuses on a specific theme or subject area such as physical phenomena like temperature variation, rainfall distribution and population density in an area.

In dot method maps, dots are typically used for rural population, while urban population is often represented by circles of varying sizes to indicate the magnitude of the population in specific urban centers.

Following steps are used to prepare isopleth maps:-

• By considering the highest and lowest values of the variable.
• The class interval is decided to draw the isopleths maps which in turn decides the difference between the lines.
• Lines are drawn for the decided intervals, location with the same value are joined by a line

Lines joining places of equal temperature are called as Isotherms.

Isopleth method is used to show the distribution of altitude, temperature, rainfall etc in a map. Isopleths are lines of equal value in the form of quantity, intensity and density. They are drown as contour lines at some selective interval. The spacing of lines express the rate of variation. If the  lines appear much apart, variation is gentle and when they are closely set, variation is sharp. 

Cartography is generally considered to be the the science and art of designing, constructing and producing maps. It includes every operation from original field-work to final printing and marketing of maps. In modern time  cartography, is also treated as a science of human commutation. 

The term isopleth is derived from two words isos + plethron; isos meaning same and plethron means measure. Thus, isopleths are the imaginary lines of equal value in the from of quantity, intensity and density. They are drown as contour lines at some selected interval. The spacing of lines express the rate of variation. 

A line on a map joining places of equal elevation is called a contour.

Close contour lines on a map indicates steep slope.

The horizontal distribution of pressure is shown by isobars. Isobars are imaginary lines joining the places having equal values of pressure. For convenience all the pressure are converted to sea level. The spacing of isobars indicates the rate and direction of the pressure. 

Contour lines showing a uniform, steep slope on a map will be evenly spaced, but close together. Remember, the closer the contour lines, the steeper the slope.

An isohaline is a line on a map connecting points of equal salinity. Other options refer to different measurements: isohyets for rainfall, isotherms for temperature, and isobars for atmospheric pressure.

Red colour is used in the topographical map to show grid lines and their numbering, man-made features such as settlements, roads and cart tracks.

In standard topographical map conventions, green is used to represent vegetation, including forests, grasslands, orchards, and shrubs. Yellow typically represents agricultural land.

A topographic map is a detailed and accurate illustration of man-made and natural features on the ground such as roads, railways, power transmission lines, contours, elevations, rivers, lakes and geographical names. The topographic map is a two-dimensional representation of the Earth's three-dimensional landscape.

Blue color is used in the topographical map to show water bodies like perennial river, canal, well, tank and spring.

Brown  colour is used in the topographical map to show contour lines and their numbering, sand dunes, highlands and stony wastelands.

White colour is used in the topographical map to show rocky or bad lands, uncultivated lands.

The contour lines drawn like a inverted V, which decreases inwards is used to represent a V-shaped valley.

A spot height is an exact point on a map with an elevation recorded beside it that represents its height above a given datum. In the UK this is the Ordnance Datum. Unlike a bench-mark, which is marked by a disc or plate, there is no official indication of a spot height on the ground although, in open country, spot heights may sometimes be marked by cairns. In geoscience, it can be used for showing elevations on a map, alongside contours, benchmarks, etc.

The triangulated height is generally used to indicate mountain peak.

Sopt height is represented by a dot in the map.

The height of a triangulation point is called a triangulated height.

In steep slopes the difference between maximum and minimum height is represented by letter 'r' which indicates relative height.

Circular contours drawn at regular distances with increase in value towards its center represent a hill.

Contour lines are the line on a map joining points of equal height above or below sea level. When contour lines are closer to each other, then slope is called steep slope. When contour lines are further apart from each other, then slope is gentle slope.

In Indian topographical maps, the Hindi term 'Nadi' is used to denote a river. 'Nala' refers to a stream or watercourse, while 'Piao' is a water station.

A long and narrow highland sloping steeply downwards on its sides with a number of summits is called a ridge.

The line that separates two adjacent drainage basins is called a water divide.

The term 'Talab' is the standard Hindi word for a tank or pond used in topographical mapping. 'Nadi' is a river and 'Nala' is a stream.

A drainage pattern with streams spreading out in all directions like spokes of a wheel is called radial drainage.

Elongated and closely spaced contours are drawn to represents ridge.

A dendritic drainage pattern is the most common form and looks like the branching pattern of tree roots. It develops in regions underlain by homogeneous material. That is, the subsurface geology has a similar resistance to weathering so there is no apparent control over the direction the tributaries take.

A 'Tahsil' or 'Taluk' is an administrative division in India, often managed by a tehsildar responsible for revenue collection. This term is standard in administrative mapping.

A rectangular drainage pattern with streams flowing parallel to each other and joining the main stream at right angle is called trellised drainage pattern.

A cuesta is a hill or ridge with a gentle slope (backslope) on one side, and a steep slope (frontslope) on the other.

While
studying different landforms on the surface of the earth, one has to
take into consideration various facets of landforms like altitude,
relief , slope, the direction of slope and the drainage. For this, maps prepared using particular methods are used. These are known as contour maps.

Contour
maps help us to understand the characteristics of the landforms. These maps are of immense use to mountaineers, trekkers, soldiers, defense
officers, etc. These maps prove to be of great use in the planning for a
region too.

For
farmer to take consideration of various facets of landforms like altitude,
relief, slope, the direction of slope, and the drainage. For this, contour maps help the farmers to understand the above characteristics of the landforms. These maps prove to be of great use in the planning for a
region too.

Man made features like settlements, roads and cart track represent red colour on topographical sheets or topographical maps.

A topographic map is a type of map that shows Height that you can measure.

Yellow color on Survey of India topographical sheets is used to denote agricultural land. Forests are shown in green, and water bodies are shown in blue.

The color brown is used to denote most contour lines on a map, which are relief features and elevations. Topographic maps use green to denote vegetation such as woods, while blue is used to denote water features like lakes, swamps, rivers, and drainage.

Topographical maps are maps that show great details of Natural and Man-made features of a small area.

Contour lines are lines drawn on a map connecting points of equal elevation. If we walk along contour line we neither gain or lose elevation. The contour line represented by the shoreline separates areas that have elevations above sea level from those that have elevations below sea level.

Contours that are numerous, closely spaced, and represent high elevations (over 1000 meters) indicate steep, rugged terrain characteristic of mountainous areas.

Toposheet is a map which provides information of all the main topographical features with specified legend and symbology with various scales of maps according to user requirements. This data acts as a baseline data for any geographical related studies.

In the Indian toposheets, the settlement are shown in Chinese vermilion colour.

Toposheet numbering systems, such as the Survey of India system, use codes to identify specific geographic regions of the country. These numbers allow users to locate the exact area covered by the map.

Marginal information is also called primary information. This information can be obtained from the margin of the sheets. The name of the state to which the area belongs is given at the top of the sheet. The year when the area was surveyed is also mentioned. The number of the sheet, the direction of magnetic variation and true north position is given at the top right corner of the sheet.

Wide spacing between contour lines indicates a gentle slope or flat terrain, which is characteristic of a plain. If there are no contours, the area is likely completely flat.

Contour lines are useful because they allow us to show the shape of the land surface
(topography) on a map. The two diagrams below illustrate the same island. The diagram on the left is a view from the side (cross profile view)such as you would see from a ship offshore.

The
typical colour for topographic maps depicts contours in brown, bodies
of water in blue, boundaries in black, and grids and roads in red.
Topographic maps may use different colours to represent area features.
Most topographic maps will use green for vegetation or national parks
and wildlife management areas.

The characteristics of contour lines which help in plotting or reading a contour map are as follows;
1) Contour lines must close, not necessarily in the limits of the plan.
2)
The horizontal distance between any two contour lines indicates the
amount of slope and varies inversely on the amount of slope.
3) Widely spaced contour indicates a flat surface.
4) Closely spaced contour indicates a steep slope ground.

Contour lines are used to represent various landforms, including steep slopes (lines close together), gentle slopes (lines far apart), and summits (closed concentric circles). Therefore, all these features are characterized by contour lines.

On topographical maps, contour lines are generally categorized into three types: index contours (thickened lines), intermediate contours (thinner lines), and supplementary contours (dashed lines).

Meridians of longitude are imaginary lines running from the North Pole to the South Pole, perpendicular to the equator and lines of latitude.

A grid is a network of intersecting horizontal and vertical lines used on maps to provide a coordinate system for locating specific points.

Usually maps are prepared in such a manner that the north direction is at the top of the map and the South side is at the bottom.
In some special cases maps may be made with the South side on the top or on the left side.

Pandharpur (Maharashtra), Gulbarga (Karnataka), Kottagudem (Telangana), and Vishakhapatnam (Andhra Pradesh) follow a general west-to-east progression across the Indian peninsula.

Comparing the latitudes of the cities, Raipur (approx 21.2 N) is further south than Bhopal (approx 23.2 N), Kolkata (approx 22.5 N), and Udaipur (approx 24.5 N).

The Survey of India is the national mapping agency responsible for producing and maintaining topographical maps for the country.

Zoji La is about 100 km from Srinagar, the capital of the Union territory of Jammu and Kashmir, and 15 km from Sonmarg. It provides a vital link between Ladakh and Kashmir Valley.