Measuring the Transportation / Land Use System

Four major categories of variables are measuring the transportation / land use system:

• Administrative Divisions. Most data is gathered along a spatial framework, which corresponds to administrative divisions. Since the space over which the transportation / land use modeling process is undertaken is administered in one way or another (is it possible to find any portion of space that is not claimed to be administered by a form of institution?), this political attribute is of significant consequence. The data collection process inherits the established zoning, such as census districts, counties, or municipalities, to name a few. In some cases, administrative divisions are politically convenient and structured, but may undermine the validity or relevance of transportation / land use modeling. On the above figure, section A represents a city divided in six administrative divisions (i1 to i6), in which data is acquired and maintained by governmental agencies. It is possible for the modeling process to redefine the divisions of space, but costs are also significantly increased, because the data gathering process would have to be started from scratch.
• Land Use. This type of information is commonly maintained as zoning maps, where the formal or functional (preferably) characteristics of the territory are defined. Although this data is mostly qualitative, it is of high relevance since it links spatial information, such as administrative division-related information, to a tangible geographic reality. In section B, the city is characterized by four types of land use (L1 to L4). If we assume that land use type L1 is commercial, it is logical to conclude that any commercially related data concerning administrative division i4 involves a very specific area.
• Traffic. This type of information pertains to maintain, validate and update a spatial interaction matrix. Commonly, the centroid of an origin-destination matrix, is an abstraction of an administrative division, as centroid T6 is an abstraction of administrative division i6 (section C). It is "assumed" that all traffic coming from or going to i6 is generated or attracted by centroid T6. Traffic between centroids is also a component of this matrix, where T32 would represent traffic between zone i3 and i2 and T32 would present the opposite. It is also possible to use an index k identifying a mode, if the transportation system is multimodal, which is almost always the case.
• Transportation Network. This type of information is related to the characteristics and structure of transportation infrastructures. The network is commonly represented as a geometric construct composed of nodes and segments. In the case of a multimodal network, such as the one portrayed on section D, there are two types of segments and intermodal nodes (Ikl) are possible.