Map data for Center for HCI Projects

Some tips for using ArcView GIS 3.2
Layers on the map are called themes in this tool. Themes are added to a view and can be toggled on and off using the checkboxes in the view. You can also view some of the details about a theme by running Theme, Properties. The selected theme with the gray box determines which theme to use when getting information about a shape, editing a shape, etc.

Chosing the "i" icon will give you information about a shape.

Shapes are made up of a series of points. To see the point details or to modify a shape: show the theme, select it, and choose Theme, Start Editing. Right click and shape properties will display each point's coordiantes within the shape.

Projection Information
Vector data contains coordinate values stored in the file. These coordinate values are either in the Geographic coordinate system using decimal degrees or a projected coordinate system with x and y values.

Decimal degrees can easily be converted to latitude and longitude measurements. The whole units of degrees will remain the same (i.e. in 121.135° longitude, start with 121°). Multiply the decimal by 60 (i.e. .135 x 60 = 8.1). The whole number becomes the minutes (8'). Take the remaining decimal and multiply by 60. (i.e. .1 x 60 = 6). The resulting number becomes the seconds (6"). Seconds can remain as a decimal. Take your three sets of numbers and put them together, using the symbols for degrees (°), minutes ('), and seconds (") (i.e. 121°8'6" longitude)

It seems that all Census TIGER 2000 data are in decimal degrees. TIGER data is often packaged in a data.zip file for each county. Within this file are multiple small zip files for each layer. Each smaller zip file name is a combination of a layer abbreviation (e.g. 'blk') and a 5-digit County FIPS Code (e.g. '53001') and the file extension (e.g. '.zip' or '.shp'). For example, the compressed county data layer for Cook County, Illinois would be named 'cty17031.zip'. The data layers contained within the .ZIP file contain a TIGER abbreviation prefix (i.e. 'tgr') followed by the County FIPS and layer abbreviation (e.g. 'tgr17031cty.shp'). A ReadMe file provides a listing of each prefix abbreviation.

Converting Town of Blacksburg files from Virginia State Plan, South Zone, North American Datum, 1983 to Latitude/Longitude:
On GIS machine in library tower, run C:/ESRI/AV_GIS30/ARCVIEW/BIN32/projutil.exe. Use "Browse" button to choose shapefiles to convert and click Next. Choose NAD_1983_Virginia_South[32047] from the drop down box as the name of the projected coordinate system and Foot_US[9003] as the units and click Next. If prompted, it's probably best not to save the projection with the shapefiles. Choose GCS_North_American_1983[4269] as the new geographic coordinate system and click Next. If prompted about different datums, choose No to continue with the projection. Select the directory where you want to place the new files and click Next. Verify the information and click Finish. After a little while there will be a message informing you that the projection has finished.

Projected Coordinate System
A number of parameters are used to describe a projected coordinate system including the type of projection, the coordinate system, central meridian, central parallel, false easting and northing (convenient corrections for x, y coordinates), spheroid, and datum. Geodetic datums define the size and shape of the earth and the origin and orientation of the coordinate systems used to map the earth. Datums have evolved from those describing a spherical earth to ellipsoidal models derived from years of satellite measurements. The datum is related to the SPHEROID parameter in a projection. The most common datum are the NAD 1983 which is based on the 1980 Geogetic Reference system (GRS) spheroid and reflects new satelite imagery of the earth, and the NAD 1927 which is based on the 1866 Clarke spheroid.. Although data in geographic coordinates (lat/long or decimal degrees) do not have projection or parameters, they do have to be referenced to a particular datum. EXAMPLE COMMON PROJECTIONS: Lambert conformal Conic, Albers, Tranverse Mercator (including Universal Transverse Mercator or UTM)

GIS data often has a file that contains metadata. A .prj file is often associated with a shapefile and contains the projection information. An Arc/Info converage often contains a PRJ.ADF file that has similar data. These are both text files that can be read.

A Geographic coordinate system will look something like this:

GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137,298.257222101]],PRIMEM["Greenwich",0],UNIT["Degree",0.0174532925199433]]

While a projected data set will often look like this:

Projection UTM
Zone 17
Datum NAD27
Zunits NO
Units METERS
Spheroid CLARKE1866
Xshift 0.0000000000
Yshift 0.0000000000
Parameters

Or

PROJCS "Custom"
GEOGCS "GCS_North_American_1983"
DATUM "D_North_American_1983"
SPHEROID "GRS_1980" 6378137 298.257222101
PRIMEM "Greenwich" 0
UNIT "Degree" 0.0174532925199433
PROJECTION "Lambert_Conformal_Conic"
PARAMETER "False_Easting" 600000
PARAMETER "False_Northing" 0
PARAMETER "Central_Meridian" -109.5
PARAMETER "Standard_Parallel_1" 45
PARAMETER "Standard_Parallel_2" 49
PARAMETER "Central_Parallel" 44.25
UNIT "Meter" 1

Universal Transverse Mercator (UTM)

• UTM is a common projection for map data.
• UTM coordinates define two dimensional, horizontal, positions.
• UTM zone numbers designate 6 degree longitudinal strips extending from 80 degrees South latitude to 84 degrees North latitude.
• UTM zone characters designate 8 degree zones extending north and south from the equator.
• There are special UTM zones between 0 degrees and 36 degrees longitude above 72 degrees latitude and a special zone 32 between 56 degrees and 64 degrees north latitude.

• Each zone has a central meridian. Zone 14, for example, has a central meridian of 99 degrees west longitude. The zone extends from 96 to 102 degrees west longitude. Another example, Zone 18 extends from 72 degrees west to 78 degrees west, and covers much of the Northeast US and section of Quebec. The center of the zone is 75 degrees west longitude line which lies just west of Montreal. The map below includes a portion of the UTM grid system. Note that these grid lines diverge significantly from true north (indicated by the bounding longitude lines at 72 and 78 degrees west).

• Eastings are measured from the central meridian (with a 500km (500,000m) false easting to insure positive coordinates).
• Northings are measured from the equator (with a 10,000km false northing for positions south of the equator). The following three images are an example of determining a location in a UTM coordinate system.