Major roads were instead captured as a separate principle transportation data layer. 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.