Journal of Surveying Engineering

With increasing precision in distance measurements made by surveyors and engineers, the definition of horizontal warrants reconsideration. For many applications, horizontal distance is obtained as a right‐triangle component of slope distance using a vertical angle. Since plumb lines converge near the earth's center, and because horizontal and level surfaces are different, a precisely measured slope distance loses its integrity if not reduced correctly. This paper looks at the geometry of a slope distance reduction and describes how a horizontal/level distance is obtained from two measurement configurations; slope distance combined with elevation of endpoints and slope distance combined with zenith (vertical) angle observations. Vertical refraction is considered. Tables show the similarity of horizontal and level distances and how they differ from the right triangle component of the same slope distance. Two graphs are included to help the reader decide if systematic error caused by ignoring convergence of the plumb lines is significant. Proper reduction of horizontal distance to sea level completes the discussion.

Geographic land information systems are being developed and implemented throughout federal, state, and local government agencies and in the private sector. The variation in how these systems are being implemented is large. Institution issues and barriers restrict the effectiveness of the systems. Because of its diverse nature and networked facilities the transportation industry has a central role in the efficient development of effective land information systems, not only at the state level, but at all levels.

There has been a significant interest in the application of geographic information systems (GIS) to address the special needs of the transportation industry during the past several years. Canada has been an aknowledged early leader in the development and application of GIS, particularly in the resource area. Extensive base mapping programs were initiated at both the federal and provincial government levels. Research into the special requirements of transportation agencies has not received the same level of attention and funding in Canada to date as that evidenced in the United States. Both countries have similar requirements, although they are attacking the problems from slightly differing perspectives. There is a strong case to be made for future cooperative efforts between the two countries.

In direct contrast to the comments made by vendors throughout the automated‐mapping facilities‐management (AM/FM) industry, neither AM/FM nor geographic information systems (GIS) will improve existing practices, provide added capabilities, or produce resalable data. What the systems will do is change the human‐machine environment. Whether the impacts resulting as outgrowths of that change result in the predicted institutional benefits of coordinated decision making between infrastructure systems, or even in the coordinated behaviors required to maintain the quality of shared data bases, etc., will depend upon management commitment as well as the quality of the management decisions made, and not upon the technology.