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Representations of the Earth
Maps, GIS and Remote Sensing
Tools of the Geographer
Maps
A map is the fundamental tool of the geographer.
With a map, one can illustrate the spatial distribution (i.e., geographic pattern) of almost any kind of phenomena.
Maps provide a wealth of information.
The information collected to create a map is called spatial data.
Cartography is the art of map making
Projections—From a Sphere to Flat Maps
Projections are created by transferring points on the earth onto a flat surface. You can think of this as having a light in the middle of the earth, shining through the earth’s surface, onto the projection surface. There are three basic methods for doing this:
Cylindrical--projection surface wrapped around the Earth; point of contact is equator
Conformal projection (‘preserves’ shape of continents at equator only)
Planar--projection surface is a ‘flat’ surface against the Earth at a particular latitude or longitude
Neither Conformal or Equal Area Does not ‘preserve’ shape of continents nor provide measure
for equal area
Conic–- projection surface is a cone is placed on or through the surface of the Earth
Where the projection surface touches the Earth is the “Standard Line.”
Can be either Conformal or Equal Area
Trouble with Projections Distortion--It is impossible to flatten a round object without
distortion.
Projections try to preserve one or more of the following properties:
Area--sometimes referred to as equal area (for small areas)
Projections that preserve ‘area’ are referred to as “Equal Area” projections
Shape--usually referred to as “conformality”, again for small sections
Projections that preserve “shape” are referred to as “Conformal” projections
Direction--or “azimuthality” - cardinal directions (N,S,E,W)
PROJECTION CHALLENGES
Conformality Meridians (lines of longitude) and parallels (lines of latitude)
intersect at right angles. Shape is preserved locally on conformal maps.
Area When a map portrays areas over the entire map so that all
mapped areas have the same proportional relationship to the areas on the Earth that they represent, the map is an equal-area map.
CONFORMAL VS EQUAL AREA: Projections can be either conformal or equal area – but not both!
Projections--Cylindrical Projection
Point of contact at equator
Projections--”Developing” a Cylindrical Projection
Cylindrical Projection: A Conformal Projection
Note increasing distance between lines of latitude….why?
Why Mercator? NAVIGATION!!
In a Mercator projection, the lines of longitude are straight vertical lines equi-distance apart at all latitudes, and horizontal distances are stretched above and below the equator.
Mercator’s projection preserves exactly what sailors in the 16th century needed -- shapes and directions; they were very willing to accept the size distortion.
Projections--Polar Planar Projection
Polar Planar Projection
Projection centered on North Pole
Projections--Conic Projection
Conic Conformal Projection
CONIC PROJECTIONS
A better choice for mapping regions such as the United States is a conic projection, which projects shapes from the Earth’s sphere onto a cone.
Locations near the line where the cone is tangent to the Earth will be relatively free of distortion
Robinson projectionThe Robinson projection uses tabular coordinates rather thanmathematical formulas to make earth features look the "right" sizeand shape.A better balance of size and shape result is a more accurate pictureof high-latitude lands like Russia, Soviet and Canada. Greenland istruer to size but compressed.
http://www.youtube.com/watch?v=AI36MWAH54s
Robinson projectionRobinson projectionRobinson projection
MAP SCALE
Map Scale is the ratio of the distance between two points on the Earth’s surface and the distances between corresponding points on a map
There are several types of map scales: Verbal Scale: 1 inch = 1 mile Bar Scale: a graph depicting distances
Representative Fraction:One unit of measured distance on a map equal some
units of measured distance in the real world
REPRESENTATIVE FRACTION
Representative Fraction (RF) is the ratio between measured distances on a map and measured distances on the Earth’s surface.
RF is a unitless measure – but, both sides of the ratio must be identical units
A RF scale expressed as a ratio of 1:25,000 means that one unit measured on the map represents 25,000 units on the ground. 1 inch measured on a map represents 25,000
inches on the Earth’s Surface or… 1 cm measured on a map represents 25,000
centimeters on the Earth’s surface.
LARGE-SCALE VS SMALL-SCALE
Large-Scale Maps show very small portions of the real world, but with great detail. Large-Scale maps have small denominators
i.e., 1:12,000 or 1:10,000 Topographic maps are examples of large-scale
mapsSmall-Scale maps show very large portions
of the real world, but with minimal detail Small-scale maps have large denominators,
i.e., 1:100,000 or 1:1,000,000 Wall maps are examples of small-scale maps
LARGE SCALE TO SMALL SCALE
LARGE SCALE
SMALL SCALE
Topographic Maps
3-D Topographic Maps
Thematic maps are used to communicate geographic concepts like the distribution of densities, spatial relationships, magnitudes, movements etc.
World climate or soils maps are notable examples of thematic maps. Thematic maps show population density as colored polygons and the distribution of major earthquakes felt throughout the country. Graduated circles indicate the area over which the earthquakes were felt.
Thematic Maps:
Temperature Maps
Ethnicity Maps
Precipitation Maps
Population Maps