Cartographic Perspectives (E-Journal - North American Cartographic Information Society, NACIS)
Not a member yet
1581 research outputs found
Sort by
Improving Detail in Shaded Relief
No full textThe standard “hillshade” tool included in most GIS software suites implements a simple model of lighting with a set of assumptions that make the tool fast and easy to use. This simplified lighting model can visually degrade steep terrains, producing over-dark areas and removing important terrain detail. The underlying model can, however, be manipulated to output displays without these drawbacks. This mimics the effect of ambient light without complicating the lighting model by introducing additional light sources. This article will briefly describe the underpinnings of Lambertian shaders, then demonstrate how the traditions and assumptions built into most GIS tools can be removed to give more flexibility and control over results. Finally, shadows will be discussed as a separate addition to shaded relief
Tracing the Development of the General Land Office’s “National Map”: From Lands Surveyed to Territorial Acquisitions
No full textFrom the foundation of the republic, the government of the United States promoted western expansion through the surveying and sales of the public domain. The agency responsible over most of this period, the General Land Office (GLO), produced maps of the progress of surveying and sales on an annual basis. This article reviews a notable series, from the first “connected” map (i.e., one showing all the public lands in a single view) in 1864 until the last in 1953. In each period, the national map produced by the agency reflects the concerns of the time, as it records the preparations for the sale of the public domain for settlement. In the first decades of the connected maps, the primary thematic elements documented the work of GLO in surveying what is now called the Public Land Survey System (PLSS). These maps evolved to include a treatment of “territorial acquisitions,” which eventually became the most prominent thematic element, while still including a representation of the PLSS grid. The series’ first depictions of territorial acquisitions included an exceptional error, one of several, indicating that the Oregon Country was part of the Louisiana Purchase. Commissioner Binger Hermann expounded his understanding of the United States’ territorial history in an eighty-seven page monograph, an unusual recognition of a cartographic error, which led to corrections. The long history of this map series provides material to understand the role of maps in the history of the country
