Statement of Purpose The Data Access and Support Center (DASC) Subcommittee of the Technical Advisory Committee of the State of Kansas GIS Policy Board has compiled a list of recommended Kansas projection Standards (Table 1). These recommended standards are designed to facilitate informed use of map projections and to suggest appropriate usage for particular scales and projects. For database developers contracted by the Kansas GIS Policy Board, these recommendations shall be contract standards.
Background A map projection is used to portray all or part of the round Earth on a flat surface. This cannot be done without some distortion. Every projection has its own set of advantages and disadvantages. There is no "best" projection. A map can show one or more -- but never all -- of the following characteristics: True directions (true-directions), True distances (equidistant), True areas (equal-area), and True shapes (conformal).
Map scale is the relationship between distance on the map and distance on the ground. A map scale might be given as a graphic element (bar scale), but it usually is given as a fraction or a ratio, e.g., 1/10,000 or 1:10,000. These "representative fraction" scales mean that one unit of measurement on the map -- 1 inch or 1 centimeter -- represents 10,000 of the same units on the ground. The larger denominator (the second number) the smaller the scale. Large scale maps are 1:24,000 and larger. Intermediate scale maps occur in the 1:50,000 to 1:100,000 scale range. Small scale maps are 1:250,000 and smaller.
In general, the selection of a particular projection is greatly influenced by the characteristic(s) the user wants to preserve and the scale of the map. While there are a great many map projections, most maps that users in Kansas will encounter, only a handful will be used. Table 1, presents five common projections and their construction parameters that are recommended by the Kansas GIS Policy Board.
Recommended Projections The following presents the properties of these five projections and examples of their usage by the United States Geological Survey (USGS). Much of the information presented is taken form the brochure Map Projections, U.S. Department of the Interior, USGS, National Mapping Program. For further information, see Map Projections-A Working Manual, John P. Snyder, Geological Survey Professional Paper 1395 (Washington, USGPO, 1987, 383 pp.).
Albers Equal Area Conic (Albers) Used by the USGS for maps showing the conterminous United States or large areas of the United States. Well suited for large countries or other areas that are mainly east-west in extent and that reqire equal-area representation. Used for many thematic maps. Maps showing adjacent areas can be joined at their edges only if they have the same standard parallels (parallels of no distortion) and the same scale. All areas on the map are proportional to the same areas on the Earth (equal area). Directions are reasonably accurate in limited regions. Distances are true on both standard parallels. Maximum scale error is 1 1/4% on map conterminous States with standard paralles of 29 1/2 degrees North and 45 1/2 degrees North. Scale is true only along standard parallels. Map is not conformal or equidistant.
Lambert Conformal Conic Used by USGS for many 7.5 and 15-minute topographic maps for the State Base Map series. Also used to show a country or region that is mainly east-west in extent. One of the most widely used map projections in the United States today. Looks similar to the Albers Equal Area Conic, but graticule spacings differ. Retains conformaility. Distances true along standard parallels; reasonably accurate elsewhere in limited regions. Directions resonably accurate. Distortion of shapes and areas minimal at, but increase away from, standard parallels. Shapes on large-scale maps of small areas essentially true. Map is conformal but not equal area or equidistant.
For the USGS Base Map series for the 48 conterminous States, the standard paralles are 33 degreees North and 45 degrees North (maximum scale error for map of 48 States is 2 1/2%). For USGS Topographic Map series (7.5 and 15-minute), standard paralles vary.
Universal Transverse Mercator - UTM Zones for Kansas Used by USGS for many quadrangle maps at scales from 1:24,000 and 1:250,000. It is also used for mapping large scale areas that are mainly north-south in extent. This projection is a specialized application of the Transverse Mercator Projection. The globe is divided into sixty zones, each spanning 6 degrees of longitute, with each zone having its own central meridian. Distances are true only along the central meridian or else along two lines parallel to it, but all distances, directions, shapes and areas are reasonably accurate within 15 degrees of the central meridian. Distortion of distances, directions, and size of areas increases rapidly outside the 15 degree band. Because the map is conformal, however, shapes and angles within any small area (e.g., a 7.5' topographic map) are essentially true.
State Plane - State Plane Zones for Kansas The State Plane Coordinate System is not a projection. It is a coordinate system that divides all fifty of the United States, Puerto Rico and the US Virgin Islands into over 1220 numbered zones. Construction of a coordinate system for each zone is based on one of three projections: the Lambert Conformal Conic, the Transverse Mercator or the Oblique Mercator. The State Plane coordinate system for two zones--North and South. Each zone has an assigned USGS code number, each having a designated central origin that is specified in degrees. Generally used on 7.5 and 15-minute topographic quadrangles.
Geographic (Global Reference System) Although data may be represented in units of longitude and latitude, Geographic coordinates are not a projection. This system treats the Earth as a sphere or spheroid. The sphere is divided into 360 equal parts known as degrees. Each degree can be further subdivided into 60 minutes, each composed of 60 seconds. Often the minutes and seconds are expressed as decimal degrees. The origin for measurement of longitiue and latitude is the center of the sphere. Latitude is expressed as degrees north or south of the equator, which is 0 degrees. Values of latitude range from 90 degrees North to -90 degrees South (i.e., the North and South Poles respectively). Longitude is expressed in degrees east or west of the Prime Meridian, 0 degrees, that passes through Greenwich, England. Values of longitude range from -180 degrees West to 180 degrees East.