Mapping Concepts Guide
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Basics of mapping
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Mapping Concepts Guide
- 1. MAPPING CONCEPTS K B Bindu Assistant Professor, Department of Geography, H M College, Manjeri
- 2. In this session Earth – shape, size and measurements Representation of earth What is globe? What is map? Why map projections? Cartographical representation of map
- 3. SHAPE OF THE EARTH
- 7. 90 24 h = 3600 1 h = 150 Rotation 12 h = 1800 80 10 20 0 60 50 0 0 30 40 50 60 70 10 20 30 40 50 60 70 80 01020 30
- 9. Celestial Globes Terrestrial Globes
- 10. GLOBES - LIMITATIONS Spherical body Size Shape Measurements
- 11. 10/16/15 11 MAPS
- 12. A good map depends Goal of the map Who will read the map Where will the map be used What data will be available for the composition of the map What resources are available in both time and equipment
- 13. TYPES OF MAPS Based on Scale Scale 1: 4,000meters Scale 1:3,00 Km
- 14. Based on Usefulness Topographical maps Cadastral maps Ocean & navigational charts Commercial maps Political maps Relief maps Climatic maps
- 15. Based on representation Chloropleth maps (Using hatches/ different shading) Chorochromatic maps (Using colour fills)
- 16. Map Projections
- 17. Properties of Map Projection Conformal projections - Shape (Preserve local shape) Equal-area projections - Area (Preserve the area of displayed features) Equidistant projections - Distance (Preserve the distance between certain points) True-direction projections - Direction (Maintain the directions)
- 18. Projection types Cylindrical projections Conical projections Planar projections
- 22. Cartography ART / SCIENCE OF CREATING MAPS Cartographic design uses symbology and typography to convey geographical information in a manner which is both appealing to the eye and easily understood. A map symbol is a graphic design which represents a map feature and its characteristics.
- 23. Map Elements Title (Subject or theme of the map) Mapping Feature (The area to be represented in a map) Scale North Arrow Legend (The colours and symbols used in the map to specify the objects) Labels (Name, count, etc.)
- 24. Map Elements Title North arrow Scale Legend Mapping feature Lat-Long Values
- 25. Map Features POINT FEATURE- a single location depicted by a label E.g. Temple,church… LINE FEATURE- a continuous string of coordinates E.g. Road,railway line… AREA FEATURE- closed figure whose boundary encloses a homogenous area E.g. Districts,lakes…
- 26. Map Characteristics Map Scale Map Accuracy Map Resolution Map Extent Database Extent
- 27. • RATIO OF THE DISTANCE OF THE MAP TO THE CORRESPONDING DISTANCE ON THE GROUND CAN BE REPRESENTED IN THREE WAYS » RATIO : EXPRESSED AS A FRACTION as 1:50,000 » VERBAL : STATED IN WORDS » GRAPHICAL : SHOW AS LINE DIVIDED INTO EQUAL PARTS Map Scale
- 28. Map Accuracy Depends on Quality of source data, Map scale, Drafting skill and Width of lines Absolute Accuracy : • Relationship between geographic Position on a map and it’s real world location • Important for surveying and engineering based applications Relative Accuracy: • Refers the displacement between two points on a map compared to displacement of same points in the real world Attribute Accuracy : • Precision of attribute database linked to the map’s features
- 29. Map Resolution It refers how accurately location and shape of features can be depicted for a given map scale. Scale affects resolution
- 30. Map Extent The area on the earth’s surface represented on map. Usually defined by a rectangle large enough to include all mapped features. The size of the study area depends on the map scale. Smaller the map scale larger the area. Database Extent The database extent defines the limit of area of interest
- 31. Toposheets It depicts the elevation of an area as contours. These are large scale maps. A region is divided into number of smaller sections for detailed study. May form a part of a district or more than two. The official agency preparing maps in India is The Survey Of India. Because of its national importance the topographic maps of strategic areas are restricted for sale. Some of the scales used in the topographic sheets are 1:250,000, 1:50,000, 1:25,000
- 32. Limitations of Conventional Map Limitation of size/level of distribution Storage and updation Analysis-mostly impossible Mapping unit- width of line Attributes
Notes de l'éditeur
- Although a GIS transcends the traditional paper map, many of the principles that dictate mapping locations on the earth’s surface also apply to a GIS. Without a good understanding of the basic map concepts, it is very easy to misuse geographic data. Most GIS software will not communicate this error or even its possibilities to the user. The output thus generated will be produced without comment even though it may have error greater than the accuracy requirement of an application. It is the responsibility of the analyst to understand these limitations; this require a better understanding of mapping
- This session will briefly review the basic concepts of mapping. A detailed discussion about the earth that is its shape, size and measurements will help us to know how the earth is represented in the form of globe and map. You can also know about the different types of globe and maps used to represent the earth. We will also make you familiar with the map projections used to represent earth’s surface maintaining its properties. In the end of this session some cartographic principles regarding maps will also be introduced to you.
- The earth has been surveyed many times to help us better understand its surface features and their peculiar irregularities. The surveys have resulted in many spheroids that represents the earth. However, the earth is not exactly spherical but is closer in shape to an oblate ellipsoid, a shape which bulges around the equator. Selecting a model for a shape of the earth involves choosing between the advantages and disadvantages of a sphere versus an ellpsoid. Spherical models are useful for a small scale maps (features are small) such as world atlases and globes, since the error at that scale is not usually noticeable or important enough to justify using the more complicated ellipsoid. The ellipsoid model is commonly used to construct topographic maps and for other large and medium scale maps that need to accurately depict the land surface. A third model of the shape of the earth is called as a geoid, which is complex and more or less accurate representation of the global mean sea level surface that is obtained through a combination of terrestrial and satellite gravity measurements. Generally, a spheroid is chosen to fit one country or a particular area. A spheroid that best fit one region is not necessarily the same one that fit another region. Until recently, scientist mainly used spheroid for the representation of earth. Because of gravitational and surface feature variations, the earth is neither a perfect sphere nor a perfect spheroid. Satellite technology has revealed several elliptical deviations; for example the South pole is closer to the equator than North pole. Satellite determined spheroids are replacing the older ground-measured spheroids.
- In the spherical system, 'horizontal lines', or east–west lines, are lines of equal latitude, or parallels. 'Vertical lines', or north–south lines, are lines of equal longitude, or meridians. These lines encompass the globe and form a gridded network called a graticule. The line of latitude midway between the poles is called the equator. It defines the line of zero latitude. The line of zero longitude is called the prime meridian. For most geographic coordinate systems, the prime meridian is the longitude that passes through Greenwich, England. Other countries use longitude lines that pass through Bern, Bogota, and Paris as prime meridians. The origin of the graticule (0,0) is defined by where the equator and prime meridian intersect. The globe is then divided into four geographical quadrants that are based on compass bearings from the origin. North and south are above and below the equator, and west and east are to the left and right of the prime meridian.
- A point is referenced by its longitude and latitude values. Longitude and latitude are angles measured from the earth's center to a point on the earth's surface. Latitude and longitude values are traditionally measured either in decimal degrees or in degrees, minutes, and seconds (DMS). Latitude values are measured relative to the equator and range from -90° at the South Pole to +90° at the North Pole. Longitude values are measured relative to the prime meridian. They range from -180° when traveling west to 180° when traveling east. If the prime meridian is at Greenwich, then Australia, which is south of the equator and east of Greenwich, has positive longitude values and negative latitude values. Although longitude and latitude can locate exact positions on the surface of the globe, they are not uniform units of measure. Only along the equator does the distance represented by one degree of longitude approximate the distance represented by one degree of latitude. This is because the equator is the only parallel as large as a meridian. (Circles with the same radius as the spherical earth are called great circles. The equator and all meridians are great circles.) Above and below the equator, the circles defining the parallels of latitude get gradually smaller until they become a single point at the North and South Poles where the meridians converge. As the meridians converge toward the poles, the distance represented by one degree of longitude decreases to zero. On the Clarke 1866 spheroid, one degree of longitude at the equator equals 111.321 km, while at 60° latitude it is only 55.802 km. Because degrees of latitude and longitude don't have a standard length, you can’t measure distances or areas accurately or display the data easily on a flat map or computer screen.
- Whether you treat the earth as a sphere or a spheroid, you must transform its three – dimensional surface to create a flat map sheet. This mathematical transformation is commonly referred to as a map projection. One easy way to understand how map projections alter spatial properties is to visualize shining a light through the earth onto a surface, called the projection surface. Imagine the earth’s surface is clear with the graticule on it. Wrap a piece of paper around earth. A light at the centre of the earth will cast the shadows of the graticule onto the piece of paper. You can unwrap the paper and lay it flat. Once the data is projected onto a flat surface, the spherical values change. On a flat surface, locations are identified by x,y coordinates on a grid, with the origin of the centre of the grid . Each position has two values, the x coordinate and y coordinate. Using this notation, the coordinated at the origin are x=0 and y=0. The latitude is called as x axix and longitude is called as y axis. The horizontal lines above the origin and vertical lines to the right of the origin are assigned positive values: those below to the left are negative. The advantage of a planar system is that measures of length, angle and area are constant across the two dimensions. The longitudinal values are represented in x axis and latitudes are represented in y axis.
- Earth, the third planet of our solar system revolves around the Sun once every 365 1/4 days. The elliptical orbit of the earth varies from 91.5 million miles on January 3 called "perihelion", to 94.5 million miles on July 4 called "aphelion" for an average earth-sun distance of 93 million miles. The elliptical path causes only small variations in the amount of solar radiation reaching the earth. The Earth rotates at a uniform rate on its axis once every 24 hours. Hence it takes 24 hrs to complete one rotation and covers 3600. It means in 1 hr it covers 150 and 12 hrs for covering 1800 a day. Turning in an eastward direction the Sun "rises" in the east and seemingly "travels" toward the west during the day. The Sun isn't actually moving, it's the eastward rotation towards the morning Sun that makes it appear that way. The Earth then rotates in the opposite direction to the apparent path of the Sun. Looking down from the North Pole yields a counterclockwise direction. From over the South Pole a clockwise direction of rotation occurs. You can demonstrate this by looking down at the North Pole of a counterclockwise rotating globe. Lift the globe while keeping it spinning in a counterclockwise direction and look at it from below.
- In the classroom, maps and globe s serve both as repositories of any kinds of geographical information and as an essential means of imparting that information to students. Maps constitute a critical element of geography education. However, they do have limitations. One major limitation is that it is not possible to accurately represent the round earth on a flat surface without distorting at least on earth property, such as distance, direction, or size and shape of land and water bodies. As scale models, globes constitute the most accurate representation of Earth in terms of the properties of Earth’s surface features—area, relative size and shape, scale and distance, and compass direction are proportionately and therefore correctly represented on globes. Globes present an essential overview of Earth, and they can be very useful in the teaching of such concepts as location, spatial patterns, Earth-Sun relationships, and time. However, globes have limitations: They are cumbersome to handle and store, small-scale, and only half of Earth can be observed at once. In addition to maps and globes, graphs, diagrams, aerial and other photographs, and satellite-produced images also provide valuable information about spatial patterns on Earth. They are very diversified in the kinds of information they present and, under certain circumstances, they have classroom value as both supplements to and substitutes for globes and maps. However, they also have limitations: For instance, they may not be immediately understandable to students, who may need special instruction in their use
- Globes are the only geographical representation of earth that have no distortion. Spheres such as the earth are mapped on to a flat surface using a map projection with an inherent degree of distortion. These projections can either enforce angle preservation or area preservation. A typical scale for a globe is roughly 1:40 million. A globe is a three dimensional scale model of a spheroid celestial body such as a planet, star or moon, in particular earth or alternatively a spherical representation of the sky with the stars.A globe is usually mounted at an angle on bearings. In addition to making it easy to use this mounting also represents the angle of the planet in relation to its sun and the spin of the planet. This makes it easy to visualize how days and seasons change. Most modern globes are also imprinted with parallels and meridians so that one could (if only approximately due to scale) tell where a specific point on the surface of the planet is located There are basically two types of globes that best represent the earth. Celestial Globes – which are used to represent the stars and constellations of the night sky and record their positions with respect to each other. Terrestrial globes – which represent the earth surface. Most of the se globe represent physical or political feature of the earth.
- Globe being the standard form of representation of the earth, it has its own limitations. Because of its spherical body the actual shape of earth on a paper. They are cumbersome to handle and store and only half of Earth can be observed at once. The measurement of any feature is not possible because of its spherical shape. The globe depict small scale information of a large world. Hence the large scale study of an area is not possible.
- Maps are graphic representations of selected aspects of Earth’s surface. They represent compilations of geographic information about selected physical and human features. Using point, line, and area symbols, as well as color, they show how those features are located, arranged, distributed, and related to one another. They range in appearance and purpose from a simple freehand line drawing of how to get to a friend’s house to a complex multicolor depiction of atmospheric conditions used in weather forecasting. No single map can show everything, and the features depicted on each map are selected to fit a particular purpose. Maps can depict not only visible surface features such as rivers, seacoasts, roads, and towns, but also underground features such as subway systems, tunnels, and geographic formations. They can depict abstract features such as political boundaries, population densities, and lines of latitude and longitude.
- The quality of map is often govern by the objective of map generated, its users, availability of data etc. Different users may have different uses of map. According to their purpose different maps can be generated but availability of data is a crucial factor which determine the quality and importance of map.
- Maps can be broadly classifieds based on the scale, purpose of map and based on map representation. Based on scale maps can be broadly classified as small scale and large scale maps. Small scale – Large area, less details (eg. 1:250,000) Large scale – Small area, greater details (eg. 1:2,500)
- There are several types of maps. Each show different information. Most maps include a compass rose, which indicates which way is north, south, east and west. They also include a scale so you can estimate distances. Here’s a look at some different types of maps. Topographic maps include contour lines to show the shape and elevation of an area. Lines that are close together indicate steep terrain, and lines that are far apart indicate flat terrain. Cadastral maps Includes details of land ownership details of an area. The area features land owned by an individual or government as per survey record. Ocean & navigational charts Includes charting ocean phenomena ocean currents, tides etc. best used for charting the navigation route. Commercial maps feature the type of natural resources or economic activity that dominates an area. Cartographers use symbols to show the locations of natural resources or economic activities. For example, oranges on a map of Florida tell you that oranges are grown there. Climate maps give general information about the climate and precipitation (rain and snow) of a region. Cartographers, or mapmakers, use colors to show different climate or precipitation zones. Physical maps illustrate the physical features of an area, such as the mountains, rivers and lakes. The water is usually shown in blue. Colors are used to show relief—differences in land elevations. Green is typically used at lower elevations, and orange or brown indicate higher elevations. Political maps do not show physical features. Instead, they indicate state and national boundaries and capital and major cities. A capital city is usually marked with a star within a circle.
- Therefore, different map projections are used to depict different Earth properties (e.g., equal area projections show landmasses in correct areal proportion to one another but with distortions of shape). No single map can accurately depict all Earth’s properties, so it is essential that students know how to look at a given map and know which properties are rendered correctly and which are distorted. There are different ways of map preperation. Based on the data , objectives of map preparation and scale the method of data representation will deffer. For example the administrative area of Kerala can be best representated by Chorochromatic method where as if distribution of crops is to be depicted it is best to adopt Chorochromatic method.
- A map projection is any methods used in cartography (map making) to represent the two-dimensional curved surfaces of the earth or other body on a plane. Methods for constructing a projection may be mathematical, graphical, or geometric. Regardless of the method , in the end any projection can be express mathematically. Flat maps could not exist without map projections. Flat maps can be more useful than models globes in many situations: they are more compact and easier to store; they readily accommodate an enormous range of scales; they are viewed easily on computer displays; they can facilitate measuring properties of the terrain being mapped; they can show larger portions of the earth’s surface at once; and they are cheaper to produce and transport. These useful traits of flat maps motivate the development of map projections. A spheroid can’t be flattened to a plane any easier than a piece of orange peel can be flattened – it will rip. Representing the earth’s surface into two dimensions causes distortion in the shape, area, distance or direction of the data. A map projection uses mathematical formulas to relate spherical coordinates on a globe to flat, planar coordinates. Different type of projections cause different types of distortions. Some projections are designed to minimize the distortion of one or two of the data’s characteristics. A projection could maintain the area of a feature but alter its shape. Map projections are thus designed for specific purposes. One map projection might be used for large scale data in the limited area, while another is used for a small scale map of the world.
- A fundamental projection classification is based on type of projection surface onto which the globe is conceptually projected. The projections are described in terms of placing a gigantic surface in contact with the earth, followed by an implied scaling operation. These surfaces are cylindrical (e.g., Mercator ),conic (e.g., Albers ),and azimuthal or plane (e.g., stereographic ). Many mathematical projections, however, do not neatly fit into any of these three conceptual projection methods. Hence other peer categories have been described in the literature, such as pseudoconic, pseudocylindrical, pseudoazimuthal, retroazimuthal, and polyconic. Another way to classify projections is through the properties they retain. Some of the more common categories are Area-preserving, called equal-area or equiareal or equivalent or authalic Shape-preserving, called conformal or orthomorphic Direction preserving, called azimuthal or true-directional (but only possible from the central point) Distance preserving - equidistant (preserving distances between one or two points and every other point) Relevance to GIS maps are a common source of input data for a GIS often input maps will be in different projections, requiring transformation of one or all maps to make coordinates compatible thus, mathematical functions of projections are needed in a GIS often GIS are used for projects of global or regional scales so consideration of the effect of the earth's curvature is necessary monitor screens are analogous to a flat sheet of paper thus, need to provide transformations from the curved surface to the plane for displaying data
- Cylindrical Projections Cylindrical Equal Area Cylindrical Equal-Area projections have straight meridians and parallels, the meridians are equally spaced, the parallels unequally spaced. There are normal, transverse, and oblique cylindrical equal-area projections. Scale is true along the central line (the equator for normal, the central meridian for transverse, and a selected line for oblique) and along two lines equidistant from the central line. Shape and scale distortions increase near points 90 degrees from the central line. Behrmann Cylindrical Equal-Area Behrmann's cylindrical equal-area projection uses 30:00 North as the parallel of no distortion. Gall's Stereographic Cylindrical Gall's stereographic cylindrical projection results from projecting the earth's surface from the equator onto a secant cylinder intersected by the globe at 45 degrees north and 45 degrees south. This projection moderately distorts distance, shape, direction, and area. Peters The Peters projection is a cylindrical equal-area projection that de-emphasizes area exaggerations in high latitudes by shifting the standard parallels to 45 or 47 degrees.
- Mercator The Mercator projection has straight meridians and parallels that intersect at right angles. Scale is true at the equator or at two standard parallels equidistant from the equator. The projection is often used for marine navigation because all straight lines on the map are lines of constant azimuth. Miller Cylindrical The Miller projection has straight meridians and parallels that meet at right angles, but straight lines are not of constant azimuth. Shapes and areas are distorted. Directions are true only along the equator. The projection avoids the scale exaggerations of the Mercator map. Oblique Mercator Oblique Mercator projections are used to portray regions along great circles. Distances are true along a great circle defined by the tangent line formed by the sphere and the oblique cylinder, elsewhere distance, shape, and areas are distorted. Once used to map Landsat images (now replaced by the Space Oblique Mercator), this projection is used for areas that are long, thin zones at a diagonal with respect to north, such as Alaska State Plane Zone 5001. Transverse Mercator Transverse Mercator projections result from projecting the sphere onto a cylinder tangent to a central meridian. Transverse Mercator maps are often used to portray areas with larger north-south than east-west extent. Distortion of scale, distance, direction and area increase away from the central meridian. Many national grid systems are based on the Transverse Mercator projection The British National Grid (BNG) is based on the National Grid System of England, administered by the British Ordnance Survey. The true origin of the system is at 49 degrees north latitude and 2 degrees west longitude. The false origin is 400 km west and 100 km north. Scale at the central meridian is 0.9996. The first BNG designator defines a 500 km square. The second designator defines a 100 km square. The remaining numeric characters define 10 km, 1 km, 100 m, 10 m, or 1 m eastings and northings. The Universal Transverse Mercator (UTM) UTM is the first of two projection based coordinate systems to be examined in this unit UTM provides georeferencing at high levels of precision for the entire globe established in 1936 by the International Union of Geodesy and Geophysics projection is used to define horizontal, positions world-wide by dividing the surface of the Earth into 6 degree zones, each mapped by the adopted by the US Army in 1947 adopted by many national and international mapping agencies, including NATO is commonly used in topographic and thematic mapping, for referencing satellite imagery and as a basis for widely distributed spatial databases. Zone System in order to reduce distortion the globe is divided into 60 zones, 6 degrees of longitude wide zones are numbered eastward, 1 to 60, beginning at 180 degrees (W long) the system is only used from 84 degrees N to 80 degrees south as distortion at the poles is too great with this projection at the poles, a Universal Polar Stereographic projection (UPS) is used each zone is divided further into strips of 8 degrees latitude beginning at 80 degrees S, are assigned letters C through X, O and I are omitted Distortion to reduce the distortion across the area covered by each zone, scale along the central meridian is reduced to 0.9996 this produces two parallel lines of zero distortion approximately 180 km away from the central meridian scale at the zone boundary is approximately 1.0003 at US latitudes Coordinates coordinates are expressed in meters eastings (x) are displacements eastward northings (y) express displacement northward the central meridian is given an easting of 500,000 m the northing for the equator varies depending on hemisphere when calculating coordinates for locations in the northern hemisphere, the equator has a northing of 0 m in the southern hemisphere, the equator has a northing of 10,000,000 m Advantages UTM is frequently used consistent for the globe is a universal approach to accurate georeferencing Disadvantages full georeference requires the zone number, easting and northing (unless the area of the data base falls completely within a zone) rectangular grid superimposed on zones defined by meridians causes axes on adjacent zones to be skewed with respect to each other problems arise in working across zone boundaries no simple mathematical relationship exists between coordinates of one zone and an adjacent zone Pseudocylindrical Projections Pseudocylindrical projections resemble cylindrical projections, with straight and parallel latitude lines and equally spaced meridians, but the other meridians are curves. Mollweide The Mollweide projection, used for world maps, is pseudocylindrical and equal-area. The central meridian is straight. The 90th meridians are circular arcs. Parallels are straight, but unequally spaced. Scale is true only along the standard parallels of 40:44 N and 40:44 S. Eckert Projections Eckert IV Equal Area The Eckert IV projection, used for world maps, is a pseudocylindrical and equal-area. The central meridian is straight, the 180th meridians are semi-circles, other meridians are elliptical. Scale is true along the parallel at 40:30 North and South. Eckert VI Equal Area The Eckert VI projection , used for maps of the world, is pseudocylindrical and equal area. The central meridian and all parallels are at right angles, all other meridians are sinusoidal curves. Shape distortion increases at the poles. Scale is correct at standard parallels of 49:16 North and South. Robinson The Robinson projection is based on tables of coordinates, not mathematical formulas. The projection distorts shape, area, scale, and distance in an attempt to balance the errors of projection properties. Sinusoidal Equal Area Sinusoidal equal-area maps have straight parallels at right angles to a central meridian. Other meridians are sinusoidal curves. Scale is true only on the central meridian and the parallels. Often used in countries with a larger north-south than east-west extent.