How to read a Topographic Map? What is the difference between topographic maps and other maps? Topographic map - Represent cultural and natural features Chorographic maps - Cover large regions Planimetric maps - Do not show elevations Thematic maps - Focus on specific topics Photographic maps - Use of photo as map Digital Maps - Digitized map data Planimetric Maps Present the horizontal position of selected features but do not show relief Examples of planimetric maps are base, cadastral, line- route, and outline maps. Topographic Maps Portray the shape and elevation of the terrain. for various purposes: - selecting sites - planning highways - routing utility lines - electing dam sites -communication facilities. Topographic Maps can be classified by scale Large-scale maps (1:24,000-scale maps) useful for highly developed areas or rural areas where detailed information is needed for engineering, planning or similar purposes. Intermediate-scale maps (from 1: 50,000 to 1:100,000) cover larger areas and are especially suited for land management and planning. Small-scale maps (1:250,000, 1:500,000, and 1:1,000,000) useful for comprehensive views of extensive projects or for regional planning. Thematic Maps Thematic maps are also called geographic, special-purpose, or distribution maps. They emphasize a single topic, such as geology, climatology, or crop distribution, and the entire map is devoted to presenting this distribution. Geographers use thematic maps to show the distribution of subjects such as population, languages, crop production, soil, climate, vegetation, land use, and industry. Digital Maps Data-processing systems have made it possible to store digitized map data either in graphic form as a digital map or in numerical form as a body of data. The location and elevation of all bridges in a given area can be obtained from the data bank and automatically plotted on a map or listed in terms of horizontal and vertical coordinates. Photomaps They are an alternative to the other maps, they show nonselective details requiring photo interpretation by the user. Some people like the term Topographic Maps while others prefer Topographical Maps Both terms are correct, and mean the same thing. Definition of a map A graphic representation of a portion of the earth's surface drawn to a scale. It uses colors, symbols, and names to represent features found on the ground . Definition of a topographic map A topographic map is a detailed and accurate graphic representation of cultural and natural features on the ground The Canadian Centre for Topographic Information Definition of a topographic map is characterized by large-scale detail and quantitative representation of relief, usually using contour lines in modern mapping, but historically using a variety of methods. What is the difference between topographic maps and other maps? A unique characteristic that distinguishes topographical maps from other kinds of maps is the fact that they show the topography or shape of the land in addition to other features such as roads, rivers, lakes, etc. What is the difference between topographic maps and other maps? Contours are imaginary lines that join points of equal elevation on the surface of the land above or below a reference surface. Contours make it possible to measure the height of mountains, depths of the ocean bottom, and steepness of slopes. Why topographic maps? Because topographical maps show the shape of the land, it is the most suitable map for most outdoor activities that take place in areas that are not heavily populated. Why topographic maps? A topographic map shows more than contours. The map includes symbols that represent such features as streets, buildings, streams, and vegetation. Why topographic maps? Topographic maps represent a incredible resource for educators and learners. They can be used in a variety of ways in the science, geography, and history curriculum, from elementary to university level. Brief history In the 1670s Giovanni Domenico Cassini persuaded to make a detailed map of France. After Cassini's death, his children and grandchildren continued to labor on the project. The final result, called the Carte de Cassini, was published in 1793 and was the first accurate topographic map of an entire country. Topographic maps in Sri Lanka 1:63,360 1:50,000 1:10,000 1: 250,000 Sri Lanka One Inch Map (One mile to an inch) 72 map sheets cover the whole Island Relief Contours at 100ft. Intervals First Edition Completed in 1924 Last revision in 1985 Sri Lanka 1: 50,000 Scale 1:50,000 92 map sheets to cover the whole Island Relief -Contours at 20m /100ft intervals First Edition started in 1985 Revised Edition started in 1999 Sri Lanka 1: 50,000 Sri Lanka 1: 10,000 1834 map sheets cover the whole Island Relief - Contours at 2m /5m /10m intervals Sri Lanka 1: 250,000 4 map sheets to cover the whole Island First edition 1992 Data source - Complied from 1:50,000 maps The USGS published approximately 57,000 different topographic maps covering the USA. Reading topographic maps Features are shown as points, lines, areas and names depending on their size and extent. Interpreting the colored points, lines and areas, is the first step in reading topographic maps. Reading Topographic Maps - Areas The first features usually noticed on a topographic map are the area features, such as vegetation (green), water (blue), and densely built-up areas (gray or red). Reading Topographic Maps - Lines Many features are shown by lines that may be straight, curved, solid, dashed, dotted, or in any combination. The colors of the lines usually indicate classes of information: topographic contours (brown); lakes, streams, irrigation waterways, and other hydrographic features (blue); land grids and important roads (red); and other roads (yellow) , railroads, boundaries, and other cultural features (black). Reading Topographic Maps - Points Various point symbols are used to depict features such as buildings, springs, water tanks, mines, survey control points, and wells. Reading Topographic Maps - Names Names of places and features are shown in a color corresponding to the type of feature. Many features are identified by labels. Reading Topographic Maps - Contours Contours are shown in brown by lines of different widths. Each contour is a line of equal elevation; therefore, contours never cross. They show the simplified shape of the terrain. Index contours are wider. Elevation values are printed in several places along these lines. Intermediate and supplementary contours are narrower and found between the index contours help to show more details of the land surface shape. Reading Topographic Maps Contour lines Contours that are very close together represent steep slopes. Widely spaced contours or an absence of contours means that the ground slope is relatively level. The elevation difference between two contour lines called the contour interval. Relief Contour lines Index 200 number written on line Intermediate between Index lines Supplementary added to flat areas to show measurements Bathymetric contours Bathymetric contour They are shown in blue or black, depending on their location. They show the shape and slope of the ocean bottom surface. The bathymetric contour interval may vary on each map and is explained in the map margin. Marginal information and symbols A map could be compared to any equipment. Before it is placed into operation, the user must read the instructions. The marginal information and symbols, where useful information telling about the map, are useful for this requirement. Sheet Name It is found in bold print at the center of the top. A map is generally named for the main settlement contained within the area covered by the sheet. Sometimes, the largest natural feature located within the area is also used. Sheet Number The sheet number is found in bold print in both the upper right and lower left areas of the margin, and in the center box of the adjoining sheets diagram (Location), which is found in the lower right margin. It is used as a reference number to link specific maps to overlays, operations orders, and plans. Series Name The map series name is found in the same bold print as the sheet number in the upper left corner of the margin. Representative Fraction The scale is found both in the upper left margin after the series name, and in the left of lower margin. The scale note is a representative fraction that gives the ratio of a map distance to the corresponding distance on the earth's surface. The scale 1:50,000 indicates that one unit of measure on the map equals 50,000 units of the same measure on the ground. Linear Scales These are located in the left of the lower margin. They are rulers used to convert map distance to ground distance. Maps have two bar scales, in km and miles. Care should be exercised when using the scales, especially in the selection of the unit of measure that is needed. Series Number The series number is found in the lower left margin. For example: A.B.M.P. Edition Number The edition number is found in bold print in the lower left area of the bottom margin. Editions are numbered consecutively; therefore, if you have more than one edition, the highest numbered sheet is the most recent. The map edition date is found in the lower right margin of the map. This date is important when determining how accurately the map data might be expected to match what you will encounter on the ground. Administrative Index The index to boundaries diagram appears in the lower or right margin of all sheets. This diagram, which is a miniature of the map, shows the boundaries that occur within the map area. Adjoining Sheets Diagram - Location Maps contain a diagram called Location that illustrates the adjoining sheets. It consists of nine rectangles representing eight adjoining sheets necessary to surround the rectangle that represents the sheet under consideration. The diagram usually contains nine rectangles. All represented sheets are identified by their sheet numbers and sheet names. Elevation Guide This is normally found in the lower left margin. The elevation guide provides the map reader with information on datum, and elevation measurements. Datum for all level is the Mean Sea Level (MSL) What Is Mean Sea Level (MSL)? The height (H) above an imaginary surface called the geoid, is determined by the earth's gravity and approximated by MSL. MSL is usually described as a tidal datum that is the arithmetic mean of water elevations observed over a 19- year cycle. MSL is defined as the zero elevation for a local area. However, MSL differs from one country to another country. North This is located in the lower margin of maps and indicates the angular relationships of true north, grid north, and magnetic north. There is a note indicating the conversion of azimuths from grid to magnetic and from magnetic to grid next to the declination diagram. North MN TN GN True North True North (Geographical North) is a line from any point on the earth's surface to the north pole(900 N) All longitudes are true north lines. True north is usually represented by TN. Magnetic North Magnetic North is the direction to the north magnetic pole, as indicated by the north-seeking needle of a magnetic instrument. Approximately 11° difference exists between True North and Magnetic North. Currently located in Canada about 1,300 km from True North. Grid North Grid North is established by using the vertical grid lines on the map. Grid north may be symbolized by the letters GN or the letter. Grid North is not equal to True North. North- Declination Diagram Grid-Magnetic Angle. The GM angle value is the angular size that exists between grid north and magnetic north. It is an arc, indicated by a dashed line, that connects the grid-north and magnetic-north prongs. The GM angle is important to the map reader because azimuths translated between map and ground will be in error by the size of the declination angle if not adjusted for it. North- Declination Diagram Grid Convergence. An arc indicated by a dashed line connects the prongs for true north and grid north. The value of the angle for the center of the sheet is given to the nearest full minute with its equivalent to the nearest mil. These data are shown in the form of a grid- convergence note. Contour Interval Note This note is found in the left of the lower margin below the bar scales. It states the vertical distance between adjacent contour lines of the map. When supplementary contours are used, the interval is indicated. In recent edition maps, the contour interval is given in meters (20 meters) instead of feet. Grid Note This note is located below the Location grid of the lower margin. It gives information pertaining to the grid system used and the interval between grid lines. Projection Note The projection is the framework of the map. This framework is of the conformal type; (a) small areas of the surface of the earth retain their true shapes on the projection; (b) measured angles closely approximate true values; (c) scale factor is the same in all directions from a point. The projection note is located below the bar scale. Projection Note TRANSVERSE MERCATOR PROJECTION. Between 80° south and 84° north, maps at scales larger than 1:500,000. LAMBERT CONFORMAL CONIC PROJECTIONS Between 80° south and 84° north, maps at 1:1,000,000 scale and smaller POLAR STEREOGRAPHIC PROJECTION. Maps of the polar regions (south of 80° south and north of 84° north) at 1:1,000,000 and larger scales Cylindrical Projection Mercator Projection Cylinder tangent ^iam¾Ylh& at the Equator Transverse Mercator Projection Cylinder tangent ^iam¾Ylh& Conformal to Central meridian for shape Oblique Mercator Projection Transverse Mercator Projection Relief If you see the features on the map and you will understand how a topographic map works. The contour lines are very close together, indicating an extremely steep slope that rises from 4500 feet to 5100 feet and a circular mountain. The open center circle inside the 5100 contour line indicates that the top of the mountain is a flat plateau. A B C D Types of slope -Gentle Contour lines showing a uniform, gentle slope will be evenly spaced and wide apart . Considering relief only, a uniform, gentle slope allows the defender to use grazing fire. The attacking force has to climb a slight incline. Types of slope -Steep 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. Types of slope -Concave Contour lines showing a concave slope on a map will be closely spaced at the top of the terrain feature and widely spaced at the bottom. Types of slope -Convex Contour lines showing a convex slope on a map will be widely spaced at the top and closely spaced at the bottom. Terrain features - Hill A hill is an area of high ground. From a hilltop, the ground slopes down in all directions. A hill is shown on a map by contour lines forming concentric circles. The inside of the smallest closed circle is the hilltop Terrain features - Saddle A saddle is a dip or low point between two areas of higher ground. A saddle is not necessarily the lower ground between two hilltops; it may be simply a dip or break along a level ridge crest. Terrain features - Valley A valley is a stretched-out groove in the land, formed by rivers. A valley begins with high ground on three sides, and usually has a course of running water through it. Contour lines forming a valley are either U-shaped or V- shaped. Terrain features - Ridge A ridge is a sloping line of high ground. Contour lines forming a ridge tend to be U-shaped or V- shaped. The closed end of the contour line points away from high ground . Terrain features - Depression A depression is a low point in the ground or a sinkhole. It could be described as an area of low ground surrounded by higher ground in all directions. Usually only depressions that are equal to or greater than the contour interval will be shown. Terrain features - Draw A draw is a less developed stream course than a valley. In a draw, there is essentially no level ground and, therefore, little or no maneuver room within its confines. A draw could be considered as the initial formation of a valley. Terrain features - Spur A spur is a short, continuous sloping line of higher ground, normally jutting out from the side of a ridge. A spur is often formed by two rough parallel streams, which cut draws down the side of a ridge. Terrain features - Cliff A cliff is a vertical or near vertical feature; it is an abrupt change of the land. When a slope is so steep that the contour lines converge into one "carrying" contour of contours, this last contour line has tick marks pointing toward low ground. Terrain features - Cut A cut is a man-made feature resulting from cutting through raised ground, usually to form a level bed for a road or railroad track. Cuts are shown on a map when they are at least 10 feet high, and they are drawn with a contour line along the cut line. Terrain features - Fill A fill is a man-made feature resulting from filling a low area, usually to form a level bed for a road or railroad track. Fills are shown on a map when they are at least 10 feet high, and they are drawn with a contour line along the fill line. Using contour lines A. There are no contour lines around this location so it is relatively flat here. B is at about 11,760 feet X and Y, at about 10,800 feet. A 3 - Gradual, consistent slope B 5/ 8 - Draw or valley with stream C 13/4 - Cliff face D 12 - Hill with ridge E 9 - Spurs on a mountainside F 10 - Depression G 4/13 - Cliff face H 7 - Steeper slope high, gradual low I 1 - Consistent slope J 2 - Gradual slope high, steeper low K 11 - A saddle between two hills L 8/5 - Draw or valley with stream M 6 - Simple round hill Analyzing Physical Features on Topographic Maps How are the physical features identifiable on topographic maps? How do physical features affect population ? What forces are most active on the landscape in this area? Landslides? Floods? Erosion? Can you plan a road from point A to point B through a mountainous region. Analyzing Cultural Features on Topographic Maps What are the major economic activities of the area shown on the selected topographic map? How are these activities reflected in the cultural, or human-built, features on the map? Is this a fast or slow-growing, or declining, area, and why? What forces act to limit or promote growth? Why are certain land uses concentrated in certain areas? Site vs Situation Site refers to the physical attributes of a location. Situation refers to the advantages and disadvantages of one location over another location, considering urbanization, transportation, and so on. How to use a topographic map for site vs situation comparing two different locations. Discuss selecting a land for a planned city. Creating Aspect Maps Aspect refers to the direction (north, east, south, west) that the slope faces. Make an aspect map by examining contour lines. Compare the vegetation on north-facing versus south- facing slopes. Compare health of the people living on slopes east-facing versus west-facing. Discuss earth-sun relationships. Analysis of Humans settlements and Hydrography How do rivers encourage (e.g. transport) and discourage (e.g. flooding) settlements? Why does place near a large river attract a large city, while the other place is sparsely populated? This may occur if one place was higher and flood-free, and the other was flood-prone. What is the elevation of both places? Location of the city of Durham, UK Castle Topographic Map Skills When reading a topographic map, you need to visualize in your mind's eye a 3- dimensional view of what the symbols and contour lines are representing. Using a Map and Compass If you understand how to read a compass and how to read a map, then its about time you learned to use both map and compass together. Separately, a good map or compass can be very useful, but limited. Together, they can lead you around the world but you need to know how to use them properly. How a Compass Works There is a huge magnetic field around the earth. It is huge, but it is not very strong. The magnetized needle in a compass is aligned with this magnetic field. As the image below shows, the composition of the earth acts as a huge bar magnet sitting upside down in the middle of the planet. Since its South end is at the north pole and its North end is at the south pole, the North end of a compass needle is pulled north. Map Symbols Since a map is a reduced representation of the real world, map symbols are used to represent real objects. Without symbols, we wouldn't have maps. Both shapes and colors can be used for symbols on maps. A small circle may mean a point of interest, with a brown circle meaning recreation, red circle meaning services, and green circle meaning rest stop. Colors may cover larger areas of a map, such as green representing forested land and blue representing waterways. To ensure that a person can correctly read a map, a Map Legend is a key to all the symbols used on a map. It is like a dictionary so you can understand the meaning of what the map represents.
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