Introduction to Geoinformatics I

Transcription

1 Introduction to Geoinformatics I MAP CONCEPT Definition: 1) A map is a visual representation of an area a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes. 2) A map is a picture or representation of the Earth's surface, showing how things are related to each other by distance, direction, and size. Maps are a way of showing many things about a portion of the earth's surface on a flat piece of paper that can be carried and transported easily. A map is not a photograph of the Earth's surface. It can show many things that a picture cannot show, and as a result, a map looks different in many ways from a photograph of the Earth's surface. Scale: A globe is the only way to represent the earth with constant scale throughout the entire map in all directions. A map cannot achieve that property for any area, no matter how small. It can, however, achieve constant scale along specific lines. Some possible properties are: The scale depends on location, but not on direction. This is equivalent to preservation of angles, the defining characteristic of a conformal map. Scale is constant along any parallel in the direction of the parallel. This applies for any cylindrical or pseudocylindrical projection in normal aspect. Combination of the above: the scale depends on latitude only, not on longitude or direction. This applies for the Mercator projection in normal aspect. Scale is constant along all straight lines radiating from two particular geographic locations. This is the defining characteristic an equidistant projection, such as the Azimuthal equidistant projection or the Equirectangular projection. MAP SCALES & UNITS This handout was designed to help you understand the relationships between different map scales, map units, distance, and area. You should understand the logic behind how these are used and how they should appear on real topographic maps. On your upcoming lab exam, you should also be able to convert one type of map scale into another, and calculate size differences (scale factor, area factor) between different maps. A. Review of Common Types of Map Scales All map scales are an expression of the numerical relationship between the MAP and the LAND that is represented. The MAP unit is always mentioned first. 1. Verbal Scale: The verbal scale is just a sentence stating that "1 Map Unit = X Land Units". For reasons of convenience, a mixture of units is commonly used, such as 1 inch = 1 mile

2 However, there are NO requirements that the units must be different! The expression "1 inch = 63,360 inches" is still a verbal scale. A mixture of map and land units makes the verbal scale difficult to compare between different maps - it must be converted first to a Representative Fraction (see below). 2. Representative Fraction (R.F.): An R.F. scale is a ratio, or fraction, that expresses the mathematical relationship between MAP and LAND, such as 1 : 24,000 which means "1 map unit is equivalent to 24,000 land units." Because an R.F. carries no units (inches, centimeters, etc.), it means that the R.F. scales can be compared between different maps. Converting an R.F. scale to a verbal scale is very easy; simply select ONE unit and apply it to BOTH map and land numbers. The above example can be written as a verbal scale as "1 inch = 24,000 inches" or "1 meter = 24,000 meters," etc. (Note: YOU CANNOT MIX UNITS in an R.F.! Doing so will change the numerical relationship of the R.F.) 3. Graphic Scale: The graphic scale is a bar chart or "ruler" that is drawn at the bottom of a topographic map. This is the scale that you should use when asked to measure distances on the map. Be Careful: Note that the zero mark is not located at the left end of the graphic scale. For your convenience, the graphic scale extends to the left of the zero mark to indicate fractions of units, such as 1/10 of a mile. You may measure distances by marking off the 2 end points on the edge of a sheet of paper and aligning the edge of the paper against the graphic scale (make sure one of your marks is on the zero). Types of Maps TOPOGRAPHIC MAPS Topographic maps show a 3 dimensional world in 2 dimensions by using contour lines. Many people have trouble reading these maps, because they have mountains and valleys are represented with concentric circles and lines. Many hikers use topographic maps, especially in areas where there are no roads with signs. Geologists depend on topographic maps to record the types of rocks. Engineers use topographic maps when they are planning roads, buildings, or other human made structures. Imagine designing a city without considering where hills and valleys are located!

3 GEOLOGIC MAPS A geologic map is a map of the different types of rocks that are on the surface of the Earth. By mapping different rock types, geologists can determine the relationships between different rock formations which can then be used to find mineral resources, oil, and gravel deposits. Also, you want to know what type of rock you are building on or else you might have a Leaning Tower of Pisa or a pile of rubble after a strong earthquake. Go to the activity and construct your own geologic map. BIOGEOGRAPHIC MAPS Scientists involved in the study of animals, plants, and other living organisms use maps to illustrate where these groups live or migrate. It is important to many zoologists to know where the organisms that they study live and where they move to. People who monitor endangered species need to know if the ranges of migration have become larger or smaller through time.

4 ENVIRONMENTAL MAPS These types of maps include maps that look at human's activity in urban and metropolitan areas and the environment in which we all live. Maps that illustrate physiographic features such as forests, grassland, woodland, tundra, grazing land, ocean floors, and ocean sediments could be included in this large grouping. Meteorological maps that show climate, weather and wind are types of environmental maps. Meteorologists, oceanographers, geographers, city planners, and many other professionals depend greatly on these maps to record and forecast their specific field. MAP PROJECTION Definition "A map projection is any method of representing the surface of a sphere or other threedimensional body on a plane." In other words " Conversion of 3D to 2D" The Classification and Types of Map Projection: Next to their property (equivalence, equidistance, conformality), map projections can be discribed in terms of their class (azimuthal, cylindrical, conical) and aspect (normal, transverse, oblique). The three classes of map projections are cylindrical, conical and azimuthal.the earth's surface

5 projected on a map wrapped around the globe as a cylinder produces the cylindrical map projection. Projected on a map formed into a cone gives a conical map projection. When projected on a planar map it produces an azimuthal or zenithal map projections The three classes of map projections Projections can also be described in terms of theiraspect: the direction of the projection plane's orientation (whether cylinder, plane or cone) with respect to the globe. The three possible apects of a map projection are normal, transverse andoblique. In a normal projection, the main orientation of the projection surface is parallel to the earth's axis (as in the second figure below). A transverse projection has its main orientation perpendicular to the earth's axis. Oblique projections are all other, non-parallel and non-perpendicular, cases. The figure below provides two examples. A transverse cylindrical and an oblique conical map projection. Both are tangent to the reference surface The terms polar, oblique andequatorial are also used. In a polar azimuthal projection the projection surface is tangent or secant at the pole. In a equatorial azimuthal or equatorial cylindrical projection, the projection surface is tangent or secant at the equator. In an oblique projection the projection surface is tangent or secant anywhere else. A map projection can be tangent to the globe, meaning that it is positioned so that the projection surface just touches the globe. Alternatively, it can be secant to the globe, meaning that the projection surface intersects the globe. The figure below provides illustrations. Three normal secant projections: cylindrical, conical and azimuthal A final descriptor may be the name of the inventor of the projection, such as Mercator, Lambert, Robinson, Cassini etc., but these names are not very helpful because sometimes one person invented several projections, or several people have invented the same projection. For example J.H.Lambert described half a dozen projections. Any of these might be called 'Lambert's projection', but each need additional description to be recognized. It is now possible to describe a certain projection as, for example, Polar stereographic azimuthal projection with secant projection plane Lambert conformal conic projection with two standard parallels

6 Lambert cylindrical equal-area projection with equidistant equator Transverse Mercator projection with secant projection plane. CARTOGRAPHY Cartography (from Greek Χάρτης, chartes or charax = sheet of papyrus (paper) and graphein = to write) is the study and practice of making maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively.

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