1

Chapter 2 – Coordinate Systems

1-18-2006

Week 1

2

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.

3

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

4

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.

a = semimajor axis (equatorial radius)a = semimajor axis (equatorial radius)

b=semiminor axis (polar radius)b=semiminor axis (polar radius)

f = (a-b)/a - flatteningf = (a-b)/a - flattening1/298.26 for GRS1980, and 1/298.26 for GRS1980, and 1/294.98 for Clarke 18661/294.98 for Clarke 1866

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

5

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).

6

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”)

7

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.

8

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.

9

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)

• USGS 7.5 minute quad map is based on NAD 27.

• DO NOT MESS UP WITH DATUM!!!!

10

Exercise 2• Start “ArcMap” – the program we will use very often in

this class.• Add “tn_cnty.shp” from “g:\46505650\Data\1-18-06.• 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.

11

Try different tabs and see what you can do with them.

12

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

13

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)

14

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)

15

PLSS

• Divide state into 6x6 mile squares or townships. Each township was further partitioned into 36 square-mile parcels of 640 acres, called sections

• Link for downloading PLSS from Wyoming• http://www.sdvc.uwyo.edu/clearinghouse/howto.h

tml (click on “Browse List > General> Public Land Survey System..>PLSS/Ownership)

• Exercise: download a county’s PLSS from Wyoming and load it to the ArcMap or ArcView.

16

Exercise 3 • Download TIGER Census Data from

http://arcdata.esri.com/data/tiger2000/tiger_download.cfm.• Select TN>Putnam and the following data:

– Census Tract 2000– County 2000– Line Features – Roads– Census Tract Demographics (PL94)– Census Tract Demographics (SF1)

• Click {Proceed to Download and Download file}• 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

17

Define the projection(why?)• Define

tgr47141lKA,tgr47141cty00, and tgr47141trt00 as “NAD 1983” using ArcToolbox|Data Management Tools| Projections and Transformations|Define Projection

18

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.

19

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.