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Representations of the Earth Maps, GIS and Remote Sensing

Representations of the Earth Maps, GIS and Remote Sensing

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Page 1: Representations of the Earth Maps, GIS and Remote Sensing

Representations of the Earth

Maps, GIS and Remote Sensing

Page 2: 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

Page 3: Representations of the Earth Maps, GIS and Remote Sensing

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

Page 4: Representations of the Earth Maps, GIS and Remote Sensing

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)

Page 5: Representations of the Earth Maps, GIS and Remote Sensing

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!

Page 6: Representations of the Earth Maps, GIS and Remote Sensing

Projections--Cylindrical Projection

Point of contact at equator

Page 7: Representations of the Earth Maps, GIS and Remote Sensing

Projections--”Developing” a Cylindrical Projection

Page 8: Representations of the Earth Maps, GIS and Remote Sensing

Cylindrical Projection: A Conformal Projection

Note increasing distance between lines of latitude….why?

Page 9: Representations of the Earth Maps, GIS and Remote Sensing

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.

Page 10: Representations of the Earth Maps, GIS and Remote Sensing

Projections--Polar Planar Projection

Page 11: Representations of the Earth Maps, GIS and Remote Sensing

Polar Planar Projection

Projection centered on North Pole

Page 12: Representations of the Earth Maps, GIS and Remote Sensing

Projections--Conic Projection

Page 13: Representations of the Earth Maps, GIS and Remote Sensing

Conic Conformal Projection

Page 14: Representations of the Earth Maps, GIS and Remote Sensing

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

Page 15: Representations of the Earth Maps, GIS and Remote Sensing

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

Page 16: Representations of the Earth Maps, GIS and Remote Sensing

Robinson projectionRobinson projectionRobinson projection

Page 17: Representations of the Earth Maps, GIS and Remote Sensing

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

Page 18: Representations of the Earth Maps, GIS and Remote Sensing

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.

Page 19: Representations of the Earth Maps, GIS and Remote Sensing

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

Page 20: Representations of the Earth Maps, GIS and Remote Sensing

LARGE SCALE TO SMALL SCALE

LARGE SCALE

SMALL SCALE

Page 21: Representations of the Earth Maps, GIS and Remote Sensing

Topographic Maps

Page 22: Representations of the Earth Maps, GIS and Remote Sensing

3-D Topographic Maps

Page 23: Representations of the Earth Maps, GIS and Remote Sensing

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.

Page 24: Representations of the Earth Maps, GIS and Remote Sensing

Thematic Maps:

Temperature Maps

Page 25: Representations of the Earth Maps, GIS and Remote Sensing

Ethnicity Maps

Page 26: Representations of the Earth Maps, GIS and Remote Sensing

Precipitation Maps

Page 27: Representations of the Earth Maps, GIS and Remote Sensing

Population Maps