User:Mav/Introduction to GIS notes by maveric149

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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.

Introduction to GIS notes by maveric149/Week 4
Introduction to GIS notes by maveric149/2002-02-26 Lecture
Introduction to GIS notes by maveric149/2002-03-05 Lecture
Introduction to GIS notes by maveric149/2002-03-12 Lecture
Introduction to GIS notes by maveric149/2002-03-19 Lecture

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[edit]

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[edit]

  • 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.

Military Grid Coordinate System[edit]

  • based on UTM

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State Plane Coordinate System[edit]

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.
  • based on NAD27 (now NAD83) with coordinates in feet (even though NAD83 is in meters).


Notes on Worksheet[edit]

(The numbers in the original questions have been changed)

Use http://www.colorado.edu/geography/gcraft/notes/mapproj/mapproj.html
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

NAD27 & 83 Questions
Use of quad map to measure the difference between w:NAD27 and w:NAD83 projections. How do you find the amount of shifting between these two?

In lower left corner of map states that the shift is shown by dashed corner ticks. You measure the shift with a ruler, and use the scale on the map to find the actual distance.

Blue ticks on the map neat lines represent what?

1000-meter UTM grid ticks. Noted in lower left corner of map.

Which UTM zone does 90o west fall?

180o - 90o = n x 6o
n = UTM zone 15