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Urban Dynamics: Data and Images

Temporal Urban Mapping - Definitions, Classification Scheme, Collection Criteria

    Urban databases representing built-up lands were compiled using a geographic information system from a variety of information sources. These databases represent human-induced land transformation over the history of the region in question, 100-200 year time period.

Definitions

    Urban or Built-up Land

      Urban or built-up land is defined as areas characterized by buildings, asphalt, concrete, suburban gardens, and a systematic street pattern. Classes of urban development include residential, commercial, industrial, transportation, communications, utilities, and mixed urban. Political boundaries, such as city limits, were not used to define urban limits. Undeveloped land completely surrounded by developed areas, such as cemeteries, golf courses, and urban parks is recognized within urban areas.

    Principal Transportation

      Principal transportation is defined as the roads, railroads, seaports, airports, and other transportation features that provide the infrastructure for urban development. The transportation data layer documents the evolution of principal transportation routes. Principal transportation routes are considered the network which supports the development of the urban core. Development of the urban core requires the transport of people and materials. Compilation criteria, such as connectivity, mobility, lineage and alignment were developed to accommodate limitations in historic map sources which did not explicitly define a principal route.

    Hydrography

      The hydrography data layer identifies the reservoirs and shoreline changes resulting from urbanization.

Classification Scheme

    The classification scheme adopted for temporal urban mapping is a subset of the land use and land cover (LULC) classification system described in the USGS Professional Paper 964. The Anderson scheme is a flexible hierarchical system for use at multiple levels, depending on the level of detail and scale required by the application. The Anderson Level II classification definitions were modified slightly to accommodate limitations in the historical source materials and to better categorize land use intensity. Most urban areas within the database were categorized as Level I, Urban or Built-up Land and Level II category 16, mixed urban or built-up land. When enough information was available from the source material classification was carried to Level II and III.

    Subset of the Anderson classification scheme

    Subset of the Anderson classification scheme for urban development.

Collection Criteria

    Urban or Built-up Land

      Urban areas were compiled using criteria based on either housing density, road density, spectral reflectance, or degree of land disturbance depending on the source materials. A residential density of three houses per 2.5 acres was established as the minimum level of development interpreted as urban. The extent of urban areas was determined by the existence of a dense systematic street patterns and the relative concentration of buildings.

      The Transportation, Communications, and Utilities subcategory encompasses only the areas of intensive use. For example, areas delineated as airport facilities include only the runways, terminals, and parking lots, but not the surrounding open land. Major freeways and highways were not delineated unless they were surrounded by urban development. Major roads were instead captured as a separate principle transportation data layer.

      All areas identified as built-up, where individual uses could not be separated using the available source material, were assigned to the Mixed Urban or Built-up category 16. Land with less intensive use, such as urban parks, golf courses, cemeteries, and undeveloped surrounded by built-up land was delineated as Other Urban or Built-up Land, category 17.

    Principal Transportation

      The evolutionary development of a transportation system requires that implicit and explicit compilation criteria be defined to aid in the development of a principal transportation data layer.

      Implicit compilation criteria is based on various measures that together rate the quality of a transportation route. These measures includes connectivity, lineage, mobility, and alignment.

      Connectivity is a measure that describes the level to which a route links together urban centers or other modes of transportation such as ports, railways, or airports.

      Lineage describes the documented history of a route. It refers to the historical presence of a transportation route in literature or historical events. An example of an enduring route would be the Old National Road in Maryland which became Interstate 70 and is now known as US 40.

      Mobility is a measure of the inherent road quality or design, which implies the level of service or accessibility for a particular route.

      Alignment is a measure of the rectilinear characteristics of a transportation route. One of the primary evolutionary features of roads has been based on the ability to straighten roads by overcoming geographic features that once were barriers to travel.

      The depiction of features that further the effectiveness of a transportation route reveals the significance of that route. For example, in order for an investment to be made in the construction of a bridge, the road over the bridge is probably an important one. The presence of ancillary transportation features, such as bridges, tunnels, and ferries, is one of the factors that support the application of implicit compilation criteria.

      The presence and nature of the names applied to these routes also helps determine principal transportation courses. Toponymically, the labeling of a road with its proper name may provide valuable information. For instance, names such as the "Annapolis and Baltimore Road" indicate the significance of this route as a major artery providing mobility between two major centers. The descriptive title of these routes often provides insight into their use. In fact, distinct eras favored the use of certain descriptors for their principal routes: "turnpikes," "highways," and "beltways" are signatures for their respective generations.

      Explicit compilation criteria are related to the cartographic features used on maps that reveal the significance or effectiveness of a route. The advent of modern cartography and standardized approaches through feature classification and symbolization schemes has alleviated much of the dependence upon implicit compilation criteria. It was determined that roads designated as "interstates" by the Federal Highway Administration or as "Primary highway, hard surface" on the USGS 1:100,000-scale topographic maps met capture conditions by meeting the implicit compilation criteria.

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