GEOGRAPHIC INFORMATION SYSTEMS
Lecture 10: Map Projections (cont’d)
Examples of Map Projections
- there are hundreds of standard map projections used to map the world, continents, countries and states
- you can also create your own custom map projection (so the options are limitless)
- the following examples are taken from the USGS Map Projections web site
The Globe
- a globe is a scaled physical model – not a map projection
- no distortion in shape, area, distance or direction
1) Cylindrical Projections
- Mercator Projection
- true directions – widely used for navigation (although not the shortest route)
- Miller Projection
- similar in appearance to a Mercator projection (but directions are not true)
- designed to show highest latitudes (which Mercator does not)
Copyright © Kevin Mulligan, Texas Tech University
- Transverse Mercator Projection
- line of tangency along a meridian (the central meridian)
- used for areas with a large north-south extent (e.g. Chile)
- used as the basis for the UTM coordinate system
2) Pseudo-cylindrical Projections
- Robinson Projection
- compromise projection - widely used in atlases
- it looks about right - but area, shape, distance and direction are not true
- Sinusoidal Equal Area Projection
- an equal area projection - widely used in atlases
- used to preserve relative areas on a world map
Copyright © Kevin Mulligan, Texas Tech University
3) Conic Projections
- Albers Equal Area Conic Projection
- midlatitude equal area projection (areas are correct)
- widely used to map Texas and the contiguous United States
- Lambert Conformal Conic Projection
- midlatitude conformal projection (shape of features is correct)
- widely used to map Texas and the contiguous United States
Copyright © Kevin Mulligan, Texas Tech University
4) Planer Projections
- Orthographic
- perspective views of the Earth (as it would appear from space)
- Stereographic Projection
- conformal projection (conformal means the shape of features is true)
- mostly used to map polar regions
Copyright © Kevin Mulligan, Texas Tech University
Map Projections and Coordinate Systems
- recognize that the Geographic Coordinate System is not projected
- the GCS can be referenced to many different datums (each using different ellipsoids),
but the data are not projected and the units are unprojected decimal degrees
- when we add unprojected data, ArcMap displays latitude and longitude as if latitudes are y values and
longitudes are x values in a Cartesian coordinate system (e.g. lines longitudes are parallel to one another)
- only when we apply a map projection to the data frame does the Geographic Coordinate System become a
Projected Geographic Coordinate System
Demonstration of how to apply different map projections
- right-click on Layers to open the Data Frame dialog box > Coordinate System tab.
- note the two folders…
1) Geographic Coordinate System folder – all of the Geographic Coordinate System choices in this
folder are unprojected (but they use different datums)
Unprojected Geographic Coordinate System
2) Projected Coordinate Systems folder – all of the Geographic Coordinate System choices in this
folder are projected and can be applied to map different parts of the world
Projected Geographic Coordinate System
Copyright © Kevin Mulligan, Texas Tech University
GIST 3300 / 5300
Geographic Information Systems
Map Projections (continued)
Examples of Common Map Projections
- The Globe
- Cylindrical: Mercator, Miller, Transverse Mercator
- Pseudo-Cylindrical: Robinson, Sinusoidal Equal Area
- Conic: Albers Equal Area, Lambert Conformal Conic
- Planar: Orthographic, Stereographic
Map Projections and Coordinate Systems
- Geographic Coordinate Systems (GCS)
- Projected Coordinate Systems GCS)
Geographic Information Systems
Map Projections
Geographic Information Systems
The Globe
A physical model – not a map projection
Shape – true
Area – true
Distance – true
Direction - true
Geographic Information Systems
Mercator Projection (cylindrical)
Directions are true – used for navigation
Directions do not provide the shortest route between two locations
Polar areas north or south of 85o are not present
Geographic Information Systems
Miller Cylindrical Projection (cylindrical)
Similar to Mercator – but directions are not true – not used for navigation
Polar areas north or south of 85o are present
Poles are shown as a straight line
Geographic Information Systems
Transverse Mercator Projection (cylindrical)
Distortion is minimized along a central meridian
The UTM coordinate system uses a transverse Mercator projection
Also, useful for mapping areas with a long north-south extent
Geographic Information Systems
Robinson Projection (pseudo-cylindrical)
Some distortion in shape, area, distance and direction
It looks good – used in atlases
Geographic Information Systems
Sinusoidal Equal Area Projection (pseudo-cylindrical)
Areas on the map are proportional to those on a globe
Geographic Information Systems
Albers Equal Area Conic Projection (conic projection)
Areas are true
Used to map areas in the mid latitudes (e.g. contiguous United States)
Geographic Information Systems
Lambert Conformal Conic Projection (conic projection)
Shapes are true (conformal)
Used to map areas in the mid latitudes (e.g. contiguous United States)
Geographic Information Systems
Orthographic Projection (planer projection)
Perspective view from space
Geographic Information Systems
Stereographic Projection (planer projection)
Shapes are true (conformal)
Directions are true extending from the map center
Used to map polar areas of the world
Geographic Information Systems
Coordinate systems and map projections
Geographic Coordinate Systems (GCS)
- recognize that the Geographic Coordinate System (GCS) is not projected
- the GCS might be referenced to different ellipsoids and datums
- but the data are not projected and the units are unprojected decimal degrees
Spatial Reference or Data Frame Properties Dialog
GCS unprojected
Geographic Information Systems
Coordinate systems and map projections
Projected Coordinate Systems (GCS)
- only when we apply a map projection to the data frame or the data layers
- does GCS become a projected coordinate system
Spatial Reference or Data Frame Properties Dialog
GCS projected using
North America Albers Equal Area
Geographic Information Systems