Appendix H (Informative): Relationship of Addresses to Transportation Features and Linear Reference Locations

This Appendix presents the relationship between the Address Standard and the Transportation Part (Part 7) of the Framework Data Content Standard. The Transportation Part is comprised of five sub-parts: the Transportation Base part (Part 7), and five specialized subparts: Rail, Roads, Transit, and Inland Waterways (Parts 7b through 7e). (Part 7a, Transportation - Air, was drafted but not endorsed.). The relationship is presented in three sections:

• Section H.2 sets forth the relation between addresses and transportation networks, restates the scope of the Address Standard and the transportation standard, and defines the relationship between the two standards.
• Section H.3 lists key transportation features defined in the Framework Standard Transportation Base Part and states how address classes are related to transportation features.
• Section H.4 summarizes (from Annex B of the Framework Standard Transportation Base Part) the definition of linear reference systems and their components, and shows how addresses can be expressed as linear reference locations.

Addresses are a means by which people specify the location of travel origins and destinations by reference to a transportation network. Most addresses specify locations for structures, land parcels, incidents, and infrastructure components such as poles or hydrants. None of these features are transportation segments or nodes. By relating non-transportation features to a transportation network, thoroughfare addresses enable people to locate the address using the transportation network and travel to it along network paths.

The Address Standard provides the data elements and structuresmost of them non-geometricneeded to relate people's specific travel origins and destinations to the transportation network. The Address Standard also defines certain elements needed within the Transportation Standard to describe transportation features, most notably address numbers, address ranges, and street names.

The Transportation Part of the Framework Standard defines the geometric elements and structures needed to construct transportation networks, and the non-geometric attributes needed to describe them. Transportation networks show the paths of travel from origin to destination.

Transportation networks model the thoroughfares that thoroughfare addresses refer to, the particular thoroughfare segments by which individual addresses may be grouped into address ranges, the nodes that define intersections, and the left/right side by which odd/even parities are located. Numbered Thoroughfare Addresses and some ranges are typically modeled as point events (or occasionally linear events) located along the thoroughfare segments. Intersection Addresses and most ranges correspond to nodes and segments respectively. Thus the Framework Standard Transportation Part provides the geometric elements and structures needed to relate addresses to their corresponding transportation system segments and nodes.

The Address Standard and the Transportation Part are so closely related as to be interdependent. The following principles differentiate their scopes so as to be complementary and mutually exclusive:

1. The Address Standard defines the address classes, elements and attributes, none of which are network elements and almost all of which are non-geometric, and the Transportation Part incorporates them by reference.
2. The Address Standard provides for the description of Address Reference Systems, which set forth local rules for address assignment, and form a basis for validation and quality testing of addresses. The elements of an Address Reference System may also include the following geometric components including:

• Address Reference System Extent,
• Address Reference System Axis,
• Address Reference System Axis Point Of Beginning,
• Address Reference System Reference Polyline,
• Address Reference System Range Breakpoint,
• Address Reference System Range Breakline, and
• Address Reference System Range Polygon.

1. The Transportation Part defines the geometric structures and elements needed to model thoroughfare networks, and the address standard incorporates them by reference. They include:

• transportation networks,
• nodes, and
• segments;
• point events and
• linear events.

3.1 Key Transportation Feature Definitions

The Transportation Base part (Part 7, section 5) defines several terms needed to articulate the relationship between addresses and transportation features:

• transportation system - "set of components that allow movement of goods and people between locations" (sec. 5.25)
• event - "mechanism for locating an attribute value or feature along a transportation feature." (sec. 5.4)
• Point event - "event that occurs at a single position along a linear feature." (sec. 5.12)
• Linear event - "event that occurs for an interval along the length of a feature." (sec. 5.8)
• transportation point (TranPoint) - "topological connection between transportation segments." (sec. 5.22)
• transportation segment (TranSeg) - "linear section of the physical transportation network." (sec. 5.23)
• transportation path (TranPath) - "ordered list of whole or partial...transportation segments." (sec. 5.21)
• transportation segmentation model - "set of transportation features (TranPath, TranPoint, and TranSeg) and their topological relationships which together define all possible movements through the transportation system" (sec. 5.24)
• transportation feature (TranFeature) - "representation of transportation entities that include transportation segmentation model features, as well as other features relevant to transportation" (sec. 5.20)

3.2: Representing Addresses As Transportation Features

An address can be represented within a transportation network (e.g. a road centerline model) in various ways, depending on the class of the address and how it is mapped. This subsection gives the transportation feature types that can be used to represent each address class. The feature types are defined and explained in the FGDCs "Framework Data Content Standard Part 7: Transportation." See in particular Transportation Base, Sections 5 (Terms and Definitions) and 7 (Requirements), and Part 7c: Roads.

3.2.1 Representation of a Numbered Thoroughfare Address as a Transportation Feature:

1. (If the address is mapped as a point): Point event, related to one or more transportation segments.
2. (If the address is mapped as a line or polygon): Linear event, related to one or more transportation segments.

3.2.2 Representation of an Intersection Address as a Transportation Feature:

1. One or more transportation points (TranPoints).
2. Note that for complex intersections, or where roads are represented as two or more centerlines, one Intersection Address may be represented by multiple TranPoints.

3.2.3 Representation of a Two Number Address Range as a Transportation Feature:

1. (If the range covers part of one transportation segment): Linear event, related to a transportation segment (TranSeg).
2. (If the range covers one complete transportation segment): Transportation segment (TranSeg).
3. (If the range covers more than one complete transportation segment): Transportation path (TranPath).

3.2.4 Representation of a Four Number Address Range as a Transportation Feature:

1. (If the range covers part of one transportation segment): Linear event, related to a transportation segment (TranSeg).
2. (If the range covers one complete transportation segment): Transportation segment (TranSeg).
3. (If the range covers more than one complete transportation segment): Transportation path (TranPath).

3.2.5 Representation of an Unnumbered Thoroughfare Address as a Transportation Feature:

1. (If the thoroughfare has only one segment): Transportation segment (TranSeg)
2. (If the thoroughfare has more than one segment): Transportation path (TranPath)

3.2.6 Representation of a Landmark Address as a Transportation Feature:

1. Cannot be specified within this standard. Addresses of this class have no defined relation to a transportation data model. A Landmark Address might be mapped as a point or a line or a polygon, and if represented as a polygon it might relate to zero or one or many transportation points or segments or paths.

3.2.7 Representation of a Community Address as a Transportation Feature:

1. Cannot be specified within this standard. Addresses of this class have no defined relation to a transportation data model. A Community Address might be mapped as a point or a line or a polygon, and it might relate to zero or one or many transportation points or segments or paths.

3.2.8 Representation of a USPSPostal Delivery Box as a Transportation Feature:

1. USPSPostal Delivery Box addresses have no definite relation to any transportation feature. (They could, if desired, be mapped to the post office where the box is located, and related to the post office Numbered Thoroughfare Address.)

3.2.9 Representation of a USPSPostal Delivery Route as a Transportation Feature:

1. USPSPostal Delivery Route addresses have no definite relation to any transportation feature. If the location of the delivery points were known, then Rural route and HC route addresses could be mapped as points, treated as point events, and related to a transportation segment. Overseas military addresses have no relation to any transportation feature.

3.2.10 Representation of a USPSGeneral Delivery Office as a Transportation Feature:

1. A USPSGeneral Delivery Office could be mapped to a post office, or it could be said to have no relation to any transportation feature.
2. Overseas military addresses have no relation to any transportation feature.

Linear Reference Systems and Addresses Linear reference systems specify locations by reference to a measured distance along a route within a transportation network. Linear reference systems differ fundamentally from address reference systems and coordinate reference systems, and thus offer a third way to specify address locations. Linear reference systems are used primarily in surveying and engineering, but they are also useful in address administration. Linear referencing explicitly ties an address to a specific position along its corresponding street segment. Linear reference systems are useful in visualizing address lists and building address zone information when side of street matters. Linear referencing can therefore be useful in detecting mislocated thoroughfare addresses (out of sequence or wrong parity) and erroneous ranges.

Annex B of the Transportation Base Part provides the normative classes and types needed to define linear reference systems and specify positions along curvilinear transportation features. Annex B, Section 5, defines several terms of interest:

• Position expression - "expression used to describe a position using linear referencing and comprised of a measured value (distance expression), the curvilinear element being measured, (linear element), the method of measurement (LRM), and an optional lateral offset (offset expression)."
• Distance expression - "linear distance measured along a linear element (a component of a position expression)."
• Linear element - "underlying curvilinear element along which a linearly referenced measure is taken."
• Offset - "Optional part of a linearly referenced position expression which specifies the lateral distance left or right of the linear element being measured."

Linear Reference Locations and the Address Standard. Linear reference locations must be specified by reference to a transportation network as defined in the Transportation Part of the Framework Standard. The Transportation Part defines all the elements needed to construct the network and represent addresses within it (typically as point events). The Transportation Part also defines all the elements needed to establish and document linear reference locations, such as route, point of beginning, units of measure, method of measuring along the route, etc. Because linear reference locations can be constructed entirely within the domain of the Transportation Part of the framework standard, no linear reference attributes are provided or needed within the Address Standard.