Intermodal Terminal Facilities

August 2002

GDT98Streets:
- The original digital source of line segment, such as a Census Bureau 1980 GBF/DIME File or a USGS 1:100,000 scale DLG-3.
- Scale 1: 24,000

- For line segments that originated with the USGS DLG-3 files, the FCC is based on the USGS classification code in the DLG-3 file. For line segments that originated with the 1980 GBF / DIME Files, the FCC is based on the NS code and other feature identification content of the GBF/DIME -File.

- Latitude/longitude Data: except for DIME format (ASCII) boundary files, all latitude and longitude coordinates are signed and have six decimal places. Northern latitude is positive (0 degrees to 90 degrees), southern latitude is negative (0 degrees to -90 degrees). West longitude are negative (0 degrees to -180 degrees), and longitude are positive (0 degrees to 180 degrees)

- DIME format boundary file coordinates are expressed as all positive values with six implied decimal places. Any longitude west of 180 degrees is expressed in increasing, rather than decreasing values.

Projection using latitude/longitude coordinate values with an implied 6 decimal places

All coordinates are based on the 1983 North American Datum (NAD83).

- As new streets are reported, they are added daily by digital map technicians (DMTs) working in teams assigned to specific geographic areas covering the entire nation. As DMTs work through their particular regions, they concentrate on areas that contain the largest numbers of missing addresses, usually newly developed areas. They apply address ranges to unaddressed street segments, digitized new streets, correct inaccurate segment shapes, and add exits and turn or one-way restrictions. Each addition is verified with current maps and other data.

- ARC/INFO format products are available in double precision. Precision refers to the number of bits (single - 32bits, double - 64 bits) used to store coordinate data. Coverages in double precision are slightly more accurate, but larger than those in single precision.

For more detailed information please see Geographic Data Technology Inc. 1(800) 331.7881 or email to info@gdt1.com

Army Corp of Engineers

Airport attributes were obtained from the Federal Aviation Administration's (FAA) National Airspace System Resource Aeronautical Data and the Office of Airline Information (OAI) Enplanement Data.   The FAA Data was published by the Aeronautical Information Services (ATA-100) with an Effective Date of 21 February 2002.
Horizontal positional accuracy is based on coordinate data provided in the FAA National Airspace System Resource Aeronautical Dataset (Effective 21 February 2002).  These coordinate data identify the approximate location of the Airport Reference Point (ARP) as reported by the landing facility on the NFDC (National Flight Data Center) 5010 form.  According to NFDC guidelines, the location of the ARP should be reported to a horizontal accuracy of one arc second of latitude and longitude.  However, the accuracy of these reported coordinates are not verified by FAA.  The records were loaded into a GIS and checked for any unusual or obviously erroneous locations.