# User:Mav/Introduction to GIS notes by maveric149

Introduction to GIS Notes by maveric149. Please use these notes in any way allowable by the w:GNU FDL. However, you might want to drop me a line in my talk page after you make a wikipedia article from this information, so that I don't make a similar article from the same data. I also plan on somehow marking the text in this file that has already been incorperated into wikipedia.

Coordinate Systems

• Locations can be shown in absolute or relative terms
• There are relative and absolute locations
• Use earths equator and w:prime meridian to locate things on the earth
• lat/long is not based on cultural features.
• The location of origin is not important, just the locations fixed using the origin

In order to use a coordinate system...

1. Select an origin; usually chosen in the lower left corner of map
2. Any point on map can be then specified

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Lat/long coorinates can be specified is different formats:

1. DD.MM.SSXX (degre, minute, decimal second)
2. DD.MMXX
3. DDXX(XX...) = Decimal degree

Most w:GIS systems need input of lat/long in decimal degrees

• To convert #1 to decimal degrees multiply minutes by 1'/60, multiply seconds by 1o/60. Then add the two.
• To convert from decimal degrees to #1, multiply the decimal portion of the location by 60', then multiply the decimal portion of that by 60. Your answer sould be in DD.MM.SSXX.

## UTM

UTM was created in order to reduce the inherent distortion in w:geographic w:projections. It is based on a w:transverse w:Mercator projection. With the earth "wrapped" in a cyllindar and the w:tangent line touching one of 60 transverse Mercator projections.

• Used

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• UTM stretches from pole to pole (up to 84N and 80S)
• Each zone is 6o wide (60 zones).
• UTM zone 1 starts at the w:International Date Line
• Goes counterclockwise around the globe (looking down from the N Pole)

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### Using UTM

• Transverse line is centered in the middle of each zone.
• the only place true North and grid north exactly correspnd is at the central meridian of the UTM zone.
• UTM coordinates are specified as eith eastings (x) and northings (y)
• equator is the y in the northern hem. In the southern hemisphere the South Pole is the y coordinate origin. The max meters of a northing in 10 million (half of the 20 million meters pole to pole)

A false origin is est. for x coordinates west of western limit (alows overlap of zones for military applications)

• All eastings therefore can be given as positive numbers.
• Central meridian is given the value of 500,000 meters easting.
• Anything west of the UTM central meridian (<500,000 meters easting) has a grid north that is west of True North. It therefore has a w:declination a certain number of degrees west. Same for east.

• based on UTM

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### State Plane Coordinate System

Used in US in most every states since 1930's by surveyors for property boundaries and engineering projects.

• Developed to used as a local reference system.

## Notes on Worksheet

(The numbers in the original questions have been changed)

Cylindrical Equal Area projection

Characteristics: straight meridians and parallels (meridians equally spaced, parallels unequal. Scale along central line is distortion-free. Uses cylindrical shape. Shape & scale distortions increase near points 90 degrees from central line. Other examples; Behrmann cylindrical Equal Area, gall's Stereographic Cylindrical, Peters Cylindrical.

Azimuthal Equidistant projection

Characteristics: Used to show air-route distances. Distortion-free at Azimuthal point (which is the central point on the map). Distortion increases as you move away from central point. Other examples of Azimuthal projections; Lambert Equal Area, Oblique Aspect Orthographic, North Pole Stereographic

Albers Equal Area Conic projection

Characteristics: Distorts scale/distance everywhere except along standard parallels, Used for large nations that extend more in east / west directions than North / South. Distortion-free at standard meridians. Anything off of standard meridian is distorted. Examples of other Conic projections are; Equidistant, Lambert Conformal, and Polyconic.

Longitudinal range of UTM zone 23
Equation to find Western Boundary

180-[(n-1) x 6o] = xo

Equation with 23 for n

180-[(23-1) x 6o] = 48o

Equation to find Eastern Boundary

180-(n x 6o) = xo

Equation with 23 for n

180-[(23-1) x 6o] = 42o

Range is therefore:

42o West to 48o West

UTM Zone Questions
Number of w:meters wide for any UTM Zone at the equator (at the equator, every degree w:longitude is 111.11 kilometers)

111.1 kilometers/degree x 6o = 666.666 kilometers
666.666 km x 1000 m/km = 666,666 meters

Point on UTM Zone with easting of 400,000 meters. Grid declination is what?

West

Point on UTM Zone with easting of 560,000 meters. Grid declination is what?

East