# 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.

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...

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

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Lat/long coorinates can be specified is different formats:

- DD.MM.SSXX (degre, minute, decimal second)
- DD.MMXX
- 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 1
^{o}/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 6
^{o}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 6^{o}] =*x*^{o}

Equation with 23 for *n*

- 180-[(
*23*-1) x 6^{o}] = 48^{o}

*Equation to find Eastern Boundary*

- 180-(
*n*x 6^{o}) =*x*^{o}

Equation with 23 for *n*

- 180-[(
*23*-1) x 6^{o}] = 42^{o}

*Range is therefore:*

- 42
^{o}West to 48^{o}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 6
^{o}= 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 90^{o} west fall?

- 180
^{o}- 90^{o}=*n*x 6^{o} *n*= UTM zone 15