Understanding MultiNet
Parent topic: Understanding MultiNet

Features

A Feature is the GDF representation of a real-world object. All represented objects are related to the road environment. The road environment, however, covers a large field of topics.

A Feature Theme is a compilation of Features that share a common property.

Feature Class Name: A Feature or Feature Theme has a name that is derived from a term commonly used in everyday life.

Feature Class Code: GDF refers to a Feature or Feature Theme by a numeric code rather than by name. A code list (allcodes) database is included in your MultiNet delivery.

Feature Representation - Level 0

At level 0, real-world features are represented by a set of geometric primitives:
  • Nodes: zero-dimensional geometry that is represented by only one coordinate pair;
  • Edges: one-dimensional geometry, a linear sequence of at least two coordinate pairs;
  • Faces: two-dimensional geometry represented by a polygon.
In level 0, geometry is built according to a planar graph model: edges are split when crossing each other or when crossing faces. This is the geometric foundation on which topology is built and features are constructed.

In MultiNet® Shapefile format, Level 0 is not present or available explicitly, but is part of the internal (invisible) structure of the Shapefile format.

Feature Representation - Level 1

Level 1 objects (also called simple features) form integrated systems, such as a road network or a land use area. Topologically related nodes and edges form higher objects in a mathematical or logical network, with information about the connectivity between them.

For example, edges can build up Road Elements that are connected when sharing a "Junction" Point Feature at the same level.
  • Point features (e.g., City Centers) are constructed from nodes.
  • Line features (e.g., Transportation elements) are constructed from edges.
  • Area features (e.g., Administrative Areas) are constructed from faces.
Features are collected into feature classes by assigning a Feature Class Code to them. For example, a Transportation Element can be a Road Element (Feature Class Code 4110), a Ferry Element (4130) or an Address Area Boundary Element (4165).

Feature Representation - Level 2

Level 2 objects (also called Complex Features) do not directly contain any geographic topology. Complex Features are present whenever a feature is built of several lower-level features.

Level 2 is often a simplification of Level 1 because functionality is more important. In the figure below, the simplified Level 2 graphic reprents how a customer could display geometry based on the data that TomTom supplies:

Figure: Feature Levels 0, 1 and 2

Administrative Areas

All higher-level Administrative features (i.e., lower Administrative Order number) are complex (Level 2) features because they consist of various lower-level features. Sub-municipality settlements (Order 9) or municipalities (Order 8) are Area features that are grouped into higher-level Administrative features.

Roads (Level 2)

As with Administrative Area Complex Features, Roads consist of various lower-level features. In addition to objects associated with lower-level geometry, an Intersection is also an example of a Level 2 object. The topology associated with an intersection is contained in the Level 1 geometry of the roads and junctions that make up the intersection. Level 2 roads form a more generalized representation of the Road Network. Following are two figures: The first represents the lower-level components necessary to form Roads (Level 2) and intersections, and the second is a conceptual view of a Level 2 Road network.

See also How to Use Roads (Level 2) in the How to Use MultiNet® Shapefile and OSL section of this user guide.

Figure: Level 2 Roads - Components

Figure: Level 2 Roads - Conceptual

Feature Categories (GDF only)

GDF-AS field name (in documentation) = Feat_Cat

GDF-AR field name (in documentation) = FeatCat

Feature Categories are employed in GDF formats to identify the basic category that a feature belongs to. Below are the categories and codes:
Table 1.
Feature Category Code Notes
Absent Part 0 GDF-AR only
Point Feature 1  
Line Feature 2  
Area Feature 3  
Complex Feature 4  
Relationship 5 Used in Relationship Records

Some General Feature Descriptions

As an introduction to some of MultiNet®'s features, some general descriptions applicable to all formats are listed below in alphabetical order. This is only a partial list.

Administrative Areas

Administrative units are constructed topologically and hierarchically in the MultiNet® database, according to the GDF model. Complex Administrative Features consist of lowerlevel complex Features or simple Area Features (also see Level 2 earlier in this user guide). There are no overlaps or gaps between neighboring polygons, regardless of the administrative level.

At least 10 levels of Administrative Orders are defined for each country. The highest level, Order 0, is always the Country, which is made up of all lower-level units. Order 8 is also always present. The name of this level and the extension of its units are country-dependent. Order 8 is the lowest level that covers the whole territory of the country. It is especially important because many Relations between Features and the Order 8 Administrative Areas are made in the TomTom® database.

The intermediate orders from 1 to 7 and the lowest level, Order 9, may or may not be used, depending on a country’s political hierarchy. U.S. Administrative Areas:
  • Order 0: Country
  • Order 1: State
  • Order 8: County
  • Order 9: Minor Civil Division (MCD)
U.S. Census Places are Administrative Places (see below).

Administrative Places

An Administrative Place is an administrative area that does not fit into a hierarchical structure. This subdivision may lie in more than one Administrative Area.

Administrative Places may have their own hierarchy, as one Administrative Place can be entirely within, yet belong to, another Administrative Place. This Relation is expressed as a “Place within Place” relation. The Relationship relates an Administrative Place with another one that it belongs to, similar to the Relationship of an Entry Point and the POI that it belongs to.
Note: In GDF formats the Place Within Place Relationship only remains between Administrative Places and Administrative Areas (U.S. only) because Index Areas are an independent Complex Feature.
In Shapefile format, the Place Within Place Relationship is present between Administrative Places and Administrative Areas, and between Index Areas of different hierachy levels. Relationships between Index Areas and Administrative Areas no longer exist.

In Ireland, Administrative Place T is captured for each Townland and Administrative Place P is captured for each Postal Town as defined in the Geodirectory source of the Republic of Ireland.

In the U.S., Administrative Places are captured for each city represented in the latest Census Bureau TIGER® data.

Built-up Areas

A Built-up Area is an Area Feature independent from the Administrative Area structure. An Administrative Area can contain more than one Built-Up Area. A Built-Up Area corresponds to an area inside an Order 8 Area. An exception to this case is when an adjacent Order 8 Area does not contain a Center of Settlement. Then, the Built-up Area may cross an Order 8 Area.

Built-up Areas are determined geographically as a concentration of homes and buildings, mainly with a residential function. They improve map display and map readability.

The lack of an administrative value of a Built-up Area has implications for routing. The point where an urban speed limit applies does not always coincide with a Built-up Area boundary. If a Built-up Area is used for assigning travel-time weight factors to the Road Elements running through it, the assignment may produce only an estimation of the travel time.

Index Areas

Index Areas occur where administrative divisions of a country do not provide clear address selection or do not allow address selection at all. The following are examples of when Index Areas occur:
  • Where different Administrative Areas have the same name;
  • Where Administrative Areas at a different level are considered for addressing on the same level;
  • Where the names of Administrative Areas are not suitable for addressing because they are not known by the public;
  • Where the surface of an Administrative Area does not correspond with the area that is experienced as one unit for addressing;
  • Where Centers of Settlements are used for addressing;
  • Where street names are not unique within the Administrative Area.

IMPORTANT! As evidenced by the conditions above and the examples below, how an Index Area is built is directly related to how Administrative Areas, Postal Districts and other addressing and naming components are defined by individual countries and how that information is captured and stored in MultiNet® data.

Example: La Défense in Paris is an added value for address selection to the Administrative Order 8 Areas.

Example: The Index Area Order 8 of Brussels replaces the Administrative Area Order 8 of Brussels as this larger Area corresponds to the public perception of Brussels.

Example: The Great Britain Index Areas are based on postal information. They form a complete Index that replaces the existing Administrative hierarchy on Orders 7, 8 and 9.
Note: Northern Ireland, part of the United Kingdom, has no Index Areas. The normal Administrative Areas are sufficient for unambiguous address selection.
In short, there is no single solution or model to index building using the Index Areas that is suitable for all countries. More in-depth Index Area building examples can be found in Index Areas in MultiNet® Shapefile / OSL and Index Areas in MultiNet® GDF later in this user guide. TomTom also provides an alternative to Index Area building with the Locality Index product. See Locality Index for a brief description.

Land Cover and Land Use

In the real world, the transportation network travels through land areas of various types and uses. In a digital map, the land areas can be modeled as a continuum of adjacent areas that have a certain cover or use. Land Cover and Land Use are each a representation of the real world.
  • Land Cover represents the physical status, or natural cover, of a feature.
  • Land Use represents the human use of a feature.
The following table summarizes the differences between Land Cover and Land Use:
Table 2.
Land Cover Land Use
In the real world, a Land Cover area does not necessarily have a clear extent or a definite boundary. In the digital map, therefore, the boundary may be arbitrary. A Land Use area has a definite boundary.
Land Cover areas are exclusive. A face cannot belong to more than one Land Cover Feature. For example, a Woodland cannot simultaneously also be Moor/Heathland. Land Use areas are not exclusive. A unit of Land Use can coincide with another unit of Land Use or with a unit of Land Cover.

Example: An Industrial Harbor can be part of an Industrial Area.
Land Cover Features are not section-crossing. Land Use Features may be section-crossing.
Exclaves (disconnected parts) are not allowed. Each Feature of Land Cover is composed of adjacent polygons within one section. Exclaves are allowed. One single Feature of this category may be composed of several exclaves.
  • See the “Forest and Semi-Natural Area” section of the MultiNet Data Specifications and Data Model document for defined Land Cover features in MultiNet data.
  • See the “Artificial Surface”, “Building”, “Island” and “Park/Garden” sections of the MultiNet Data Specifications and Data Model document for defined Land Use features in MultiNet data.

For suggestions on the order of displaying Land Cover and Land Use features when programming for map display, see Displaying Land Cover and Land Use Areas later in this user guide.

Points of Interest (Services)

  • The available POIs in the core MultiNet product are listed in the MultiNet Data Specifications and Data Model document;
  • The specifications for the POIs in the core MultiNet product are found in the MultiNet Points of Interest Specifications document.

Also included in the MultiNet Points of Interest Specifications document are many more POI categories and POIs only found in the MultiNet POI enhancement product.

A Point of Interest (POI), also called a “Service,” is a point representation of an activity at a specific location. “Service” represents the activity and not necessarily the building in which the activity takes place. Although the point also may serve as a destination landmark, the point does not necessarily represent an entire physical object.

A POI can be located off of the road network. In this case, the nearest transportation element or a place of entry is identified.

Figure: Entry Point for a POI

A POI also can be a central point of an area. An airport is an example of a Land Use Area also represented as a POI. For routing purposes, a Service Belonging to Service relationship is made between an entry point POI (Airline Access) and the airport POI.

Figure: Airline Access Entry Points to Airport POI

TMCs

The Traffic Message Channel (TMC) is a system of collecting, coding and broadcasting trafficrelated information. Traffic announcements are broadcast as a coded message by a Radio Data System (RDS). The coding of the information is assembled according to a uniform global standard and is independent of language. The message is always in the same format: “there is an incident caused by something on a specific road, in a specific direction, and between two locations.”

The TMC system identifies the incident location by identifying pre-determined TMC points. A Point Location is connected by means of Line Locations (roads connected as paths) within an Area Location.

See also TMCs for Shapefile usage in the How to Use MultiNet® Shapefile and OSL section of this user guide.

Parent topic: Understanding MultiNet