The coordinate system typically used to describe locations on the earth's surface (as a SPHERE) are Longitute and Lattitude -- Longitude corresponds to the X axis in planar coordinates and Latitude to the Y axis. We can use either decimal degrees [DD] (33.75) or degrees, minutes and seconds [DMS] (35 45 00)to describe global positions.

The PROJECTion commands in ArcGIS--A/I require information about both the input coordinates and the output projected (or re-projected) coordinates.  It is easy to make a typing mistake during input, so to make life easier you can create a projection file that will be used to control the projection process. In this exmaple, the file contains information about the input projection ("Geographic") and the output projection (UTM). ****  ARCGIS REQUIRES A Projection File -- but doesn't tell you what it is or how to make it! Here's what and how. ****

You can enter the following (only the CAPITALIZED text) into a text file called LLUTM.TXT.  [You can use the Notepad or Wordpad text editors in Windows(98/NT/XP/etc) to create a text file suitable for projecting. Save as TEXT ONLY (*.txt)]

INPUT    start input section
PROJECTION GEOGRAPHIC  input projection is geographic (lat long)
UNITS DMS   units are in degrees minutes seconds
PARAMETERS  (no additional parameters required for geographic)
OUTPUT    start output section
PROJECTION UTM  output projection is UTM
UNITS METERS  units are meters
ZONE 10     UTM zone 10 covers SF -- LA is in Zone 11
PARAMETERS  (no additional UTM parameters)
END  end of projection file

In the Toolbox, there is a box to enter the 'projection file' name  (its easier if you rename it to be layername.PRJ )

Workstation:  PROJECT COVER  xLATLON xUTM   LLUTM.TXT
PROJECT  [ COVER | FILE ] input  output  {projection file}
A NEW coverage (in this case xUTM)  in projected UTM coordinates will be created from the original long-lat coordinates.

A STATE PLANE EXAMPLE:

Fitting coordinates from Long/Lat to the California State Plane Coordinate System used for Land Records follows the same logic.  With Stateplane coordinates, the "DATUM" (the spheriod used to approximate the earth) is important to the process.  Most older digital maps used the North American Datum 1927 (NAD27) datum.  In recent years, the State of California is requiring that all surveys and GIS databases be converted (reprojected) into NAD 1983 (NAD83).  California has six (6) State Plane ZONES and you need to know the zone (and its A/I "code" or FIPS Code) in order to project.  For example, the City of Long Beach is in California Zone V (five).

In this example, we will project a TIGER line "coverage" (in long/lat) to State Plane NAD83 for El Dorado County (from above):

INPUT
PROJECTION GEOGRAPHIC
UNITS DD    (decimal degrees this time!!)
PARAMETERS
OUTPUT
PROJECTION STATEPLANE
UNITS FEET   (always in feet!)
FIPSZONE 403  (??? Check this first! )
DATUM NAD83
PARAMETERS
END

Workstation:  PROJECT COVER eldoradoLL eldorado83 ELNAD83.TXT