Chapter 2 – Coordinate Systems

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# Chapter 2 – Coordinate Systems - PowerPoint PPT Presentation

Chapter 2 – Coordinate Systems. 1-18-2006 Week 1. Before you start. Make sure you have a folder in G drive (student’s folder, not same as University’s student drive) If you don’t have one, create one in G drive. Keycode to this room is 25/14, or 14/25, either one.

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## Chapter 2 – Coordinate Systems

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### Chapter 2 – Coordinate Systems

1-18-2006

Week 1

Before you start
• Make sure you have a folder in G drive (student’s folder, not same as University’s student drive)
• If you don’t have one, create one in G drive.
• Keycode to this room is 25/14, or 14/25, either one.
• Better have a jump drive for yourself. You never know how long your folder will be there before someone accidentally delete your files.
• All the data and course materials are stored in G:\4650_5650\.
• If you need to sign onto the computer, use “gisuser” as name and “gisrocks” as password.
Introduction
• Same coordinate system is used on a same “View” of ArcView or same “Data Frame” in ArcMap.
• Projection - converting digital map from longitude/latitude to two-dimension coordinate system.
• Re-projection - converting from one coordinate system to another
Size and Shape of the Earth
• Shape of the Earth is called “geoid”
• The sciences of earth measurement is called “Geodesy”
• “ellipsoid” - reference to the Earth shape.

f = (a-b)/a - flattening

1/298.26 for GRS1980, and 1/294.98 for Clarke 1866

a = semimajor axis (equatorial radius)

The geoid bulges at the North Pole and is depressed at the South Pole

Geographic Grid
• The location reference system for spatial features on the Earth’s surface, consisting of Meridians and Parallels.
• Meridians - lines of longitude for E-W direction from Greenwich (Prime Meridian)
• Parallels - line of latitude for N-S direction
• North and East are positive for lat. and long. such as Cookeville is in (-85.51, 36.17).
DMS and DD (sexagesimal scale)
• Longitude/Latitude can be measured in DMS or DD,
• For example in downtown Cookeville, a point with (-85.51, 36.17) which is in DD. To convert DD to DMS, we will have to do several steps: for example, to convert -85.51 to DMS,
• 0.51 * 60 = 30.6, this add 30 to minute and leave 0.6.
• 0.6 * 60 = 36, this add 36 to seconds. Thus, the longitude is (-85o30’36”)
Exercise - convert New York City’s DMS to DD
• New York City’s La Guardia Airport is located at (73o54’,40o46’). Convert this DMS to DD.
Exercise 1 - convert New York City’s DMS to DD
• New York City’s La Guardia Airport is located at (73o54’,40o46’). Convert this DMS to DD.
• 54/60 = 0.9 and 46/60 = 0.77
• (73.90, 40.77) is the answer.
Datum
• Spheroid or ellipsoid- a model that approximate the Earth - datum is used to define the relationship between the Earth and the ellipsoid.
• Clarke 1866 - was the standard for mapping the U.S. NAD 27 is based on this spheroid, centered at Meades Ranch, Kansas.
• WGS84 (GRS80) - from satellite orbital data. More accurate and it is tied into a global network and GPS. NAD 83 is based on this datum.
• Horizontal shift between NAD 27 and NAD can be large (fig 2.10)
• DO NOT MESS UP WITH DATUM!!!!
Exercise 2
• Start “ArcMap” – the program we will use very often in this class.
• This is an ‘unprojected” shapefile. A shapefile is a layer used in ArcView/ArcGIS consisted of 3 files with extensions “dbf”,”shp”,and ”shx”
• “Unprojected” means it is still in DD (or DMS)
• Now, find out what datum this layer is based on. (Hint: R-C on tn_cnty.shp select Layer Properties/Sources). However, the true datum is not revealed until you have metadata, or projection information available.
Coordinate Systems
• Plane coordinate systems are used in large-scale mapping such as at a scale of 1:24,000.
• accuracy in a feature’s absolute position and its relative position to other features is more important than the preserved property of a map projection.
• Most commonly used coordinate systems: UTM, UPS, SPC and PLSS
UTM
• See the back of front cover for UTM zones.
• Divide the world into 60 zones with 6o of longitude each,covering surface between 84oN and 80oS.
• Use Transverse Mercator projection with scale factor of 0.9996 at the central meridian. The standard meridian are 180 km east and west of the central meridian.
• false origin at the equator and 500,000 meters west of the central meridian in N Hemisphere, and 10,000,000 m south of the equator and 500,000 m west of the central meridian.
• Maintain the accuracy of at least one part in 2500 (within one meter accuracy in a 2500 m line)
The SPC System
• Developed in 1930.
• To maintain required accuracy of one in 10,000, state may have two ore more SPC zones. (see the front side of the back cover)
• Transvers Mercator is used for N-S shapes, Lambert conformal conic for E-W direction.
• Points in zone are measured in feet origianlly.
• State Plane 27 and 83 are two systems. State Plane 83 use GRS80 and meters (instead of feet)
PLSS
• Divide state into 6x6 mile squares or townships. Each township was further partitioned into 36 square-mile parcels of 640 acres, called sections
• http://www.sdvc.uwyo.edu/clearinghouse/howto.html (click on “Browse List > General> Public Land Survey System..>PLSS/Ownership)
Exercise 3
• Select TN>Putnam and the following data:
• Census Tract 2000
• County 2000
• Census Tract Demographics (PL94)
• Census Tract Demographics (SF1)
• They come as a zip file. Within this zip file, there are 5 zip files and one readme.html.
• Put these files on your own folder (you should create a “1-18” folder within your own folder and store all your data here)
• Create a new “Data Frame” and put unzipped layers on this data frame. Rename the Data Frame as “Putnam”
• Read the “readme.html” to find out how to obtain metadata of the census data layer. It turns out this
Define the projection(why?)
• Define tgr47141lKA,tgr47141cty00, and tgr47141trt00 as “NAD 1983” using ArcToolbox|Data Management Tools| Projections and Transformations|Define Projection
Project Layers
• Insert a new “Data Frame” and name it as “UTM83”
• Within “Projections and Transformations” select “Feature | Project”
• Project the above three layers to UTM 1983NAD.
• After you click on the “ Select” from “Spatial Reference Properties”, choose “Projected Coordinate Systems” then “UTM”, “Nad 1983”.
• Select “NAD 1983 UTM Zone 16N.prj” from the list.
• Remember to check the output dataset name. You may want to change it to “tgr47141cty00_utm83.shp” to reflect the coordinate system.
• Use “Batch Project” instead of “Project” to project two layers in one time.
Layout
• Use layout to confirm the difference between UTM83 and DD
• Switch from “data view” to “layout view”
• Overlay Putnam county border maps and see the difference.