General Product Rules

The following section of this user guide is intended to cover general MultiNet^® concepts that apply to all data formats. However, any format-specific information is noted when applicable. There are several concepts governing incorporation of features, attributes and relationships into this product. Understanding these rules will help you make better use of the product.

The Coordinate System

A coordinate system is a reference system used to measure horizontal and vertical distances on a map. A coordinate system usually is defined by projection, spheroid of reference, datum, one or more standard parallels and a central meridian.

The data in this product uses a "geographic" coordinate system.

Projection

Although not a true map projection, feature location in geographic projection is based on a flat grid of latitude and longitude coordinates.

Datum

A datum is the three-dimensional reference frame that is the basis for the coordinate systems upon which feature locations are measured on the earth's surface. A datum is defined both by an ellipsoid that approximates the size and shape of the Earth, and by parameters that specify the ellipsoid's orientation. This product references the World Geodetic System 1984 (WGS84) datum, a global datum that is the reference frame used by Global Positioning System (GPS) satellites.

Units

The units of measurement in this product are degrees of longitude and latitude.

Precision

Precision refers to the number of decimal points used when representing longitude and latitude in degree units. The precision of the longitude and latitude degrees in this product is seven decimal places (EXAMPLE: 9,5044797 47,1561687).

UTF-8

UTF-8 is the abbreviation for Unicode Transformation Format-8. UTF-8 is a variable-length character encoding for Unicode. UTF-8 encodes each Unicode character as a variable number of 1 to 4 bytes, where the number of bytes depends on the integer value assigned to the Unicode character. One byte is needed to encode the 128 US-ASCII characters. Two bytes are needed for characters from Greek, Cyrillic, Armenian, Hebrew, Arabic, Syriac and Thaana alphabets. Three or four bytes are needed for Chinese and virtually all characters in common use. The first byte of a multi-byte character sequence indicates the number of bytes in the sequence.

UTF and GDF-AS

In MultiNet^® GDF-AS, a record is 80 characters long (81 with a Line Feed). For more detailed information on UTF-8, see either the MultiNet^® Shapefile, OSL GDF-AS or GDF-AR Specification documents on this documentation DVD.

Positional Accuracy

GDF attribution name abbreviation in data = AP

Shapefile and OSL field name = POSACCUR

Absolute positional accuracy refers to how closely a given feature's mapped position matches that feature's position on the earth's surface.

Positional Accuracy Codes

In MultiNet^® data, the following positional accuracy code values apply:

Positional Accuracy Code Value	Description
0	Normal: A very accurate source. Accuracy is between 5 and 25 meters.
1	Highly inaccurate: Accuracy is off by up to 100 meters.
2	Moderately inaccurate: Accuracy is off by up to several tens of meters.