GIS Course
Coordinate
system
MAP PROJECTIONS
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Map projections
• Way to represent the curved surface of the earth on
the flat surface of a map
• Hundreds of map projections
• Each map projection has advantages and
disadvantages:
 depends on the scale of the map
 depends on map’s purpose
 different projections good for small areas, areas with a
large east–west extent, or areas with a large north–south
extent
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A geographic coordinate system is a system for identifying points or areas on the surface of the earth.
Geographic
System
Projected
System
XY COORDINATE SYSTEMS:
GEOGRAPHIC COORDINATES
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Geographic System
The main geographic coordinate system is the latitude-longitude system.
Longitude (meridians)
0°longitude (prime meridian)
180°east and west
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Latitude (parallels)
0°latitude (equator)
90° north and south
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Geographic Coordinate System (GCS)
Spherical coordinates
• Angles of rotation of a radius
anchored at Earth’s center
• 80 ⁰ longitude and 40⁰ latitude
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Degrees, minutes, seconds
Pittsburgh, PA USA
40°26′ 2″ N latitude
80°0′ 58″ W longitude
Cairo, Egypt
30° 1' 59.9988‘’ N latitude
31° 14' 0.0024‘’ E longitude
Adelaide, SA AU
34°55′ 44.4″ S latitude
138°36′ 3.6″ E longitude
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Decimal degrees
1 degree = 60 minutes
1 minute = 60 seconds
40° 26′ 2″ =
40 + 26/60 + 2/3600 =
40 + .43333 + .00055 =
40.434°
Pittsburgh, PA USA
-80.016, 40.434
Adelaide, South Australia
138.601, -34.929,
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Distances
World circumference through the poles is 24,859.82 mi,
so for latitude:
1° = 24,859.82 / 360 = 69.1 mi
1′ = 24,859.82 / (360 * 60) = 1.15 mi
1″ = 24,859.82 * 5,280 / (360 * 3,600) = 101 ft
Length of the equator is 24,901.55 mi.
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Decimal Coordinate System
The latitude and longitude values in this course use degrees/minutes/seconds (DMS), but there are
other units of measure you can use. Decimal degrees (DD) are similar to DMS, except that minutes
and seconds are expressed as decimal values. Decimal degrees are generally used to store
digital coordinate information because they make digital storage of coordinates easier and
computations faster.
How to convert from DMS to DD:
This example shows the location for Edmonton, Alberta, Canada, in DMS and DD; the coordinate is 53°32'04" N (DMS).
1-Divide each value by the number of minutes or seconds in a degree:
32 minutes = 0.533333 degrees (32/60)
04 seconds = 0.001111 degrees (04/3600)
2-Add up the degrees to get the answer:
53° + 0.533333° + 0.001111° = 53.534444 DD
Therefore, the location of Edmonton can be described in DMS as 53°32'04" N or in DD as 53.534444.
Locate cities
PROJECTED (RECTANGULAR)
COORDINATE SYSTEMS
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Map projections
Features are projected onto one of three “developable” surfaces:
•No distortion where surface touches Earth
•“Secant” projection if surface pierces Earth
•“Transverse” projection if rotated 90°
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Cylindrical Projection
•Conformal projection using a cylinder tangent
at the equator
•Parallels and meridians at right angles
•Angles and shapes of small objects preserved
•The size/shape/area of large objects distorted
(scale approaches infinity at the poles)
•Web Mercator is a variation of the Mercator
projection
Example: Mercator projection (1569)
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Conic Projection
•Equivalent projection
•Uses two standard parallels
•Scale and shape are not preserved,
but distortion is minimal between
the standard parallels
•Best suited for east-to-west land
masses
Example: Albers Equal Area
Standard projection for coterminous 48 states
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Plan projection
•Compromise projection
•Neither conformal nor equivalent
•Meridians curve gently,
avoiding extremes
•Doesn’t preserve properties,
but “looks right”
Example: Robinson projection (1961)
Good compromise projection for viewing entire world
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Coordinate system for ArcGIS PRO
WGS 1984 World Mercator (Auxiliary Sphere)
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Cartesian coordinate system
• X,Y coordinates
• feet or meters
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State Plane coordinates
• Established by the US Coast and Geodetic Survey in the 1930s
• Used by U.S. local governments
• All positive coordinates in feet or meters
 originally North American Datum (NAD 1927)
 more recently NAD 1983 and 1983 HARN (High Accuracy Reference Network)
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125 zones
• At least one for each state
• Cannot join projected zones to
make larger regions
• Follow state and county
boundaries
NAD 1983 zones for the lower 48 states
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Each zone has a projection
Lambert Conformal
eastwest orientation
Transverse Mercator
northsouth orientation
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StatePlane Pennsylvania South
• End of property
(sidewalks)
• Features provided by
City Planning Department
• NAD 1983, FIPS 3702, Feet
• Lambert Conformal Conic
Projection
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StatePlane Illinois East
• Parks and buildings
• Features provided by City of
Chicago
• NAD 1983, FIPS 1201, Feet
• Transverse Mercator projection
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ArcGIS Pro: Options set coordinate system for new maps
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• Neighborhoods (StatePlane) are added first so the data frame XY coordinates will be StatePlane PA
South
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UTM RECTANGULAR COORDINATES
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UTM (Universal Transverse Mercator)
• Developed by US Army Corps of
Engineers (1940s)
• Used by U.S. military and federal
organizations (for example USGS)
• Covers world,
80°S to 84°N
• Metric coordinates
• 60 tuned transverse Mercator
projections for longitude zones, 6°wide
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Thanks