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tmap (version 0.7)

set_projection: Set and get the map projection

Description

The function set_projection sets the projection of a shape file. It is a convenient wrapper of spTransform with shortcuts for commonly used projections. The projection can also be set directly in the plot call with tm_shape. This function is also used to set the current projection information without transformation of the shape object, which is useful when this information is missing in the shape object. The function get_projection is used to get the projection information.

Usage

set_projection(shp, projection = NULL, current.projection = NULL,
  transform = !is.null(projection), overwrite.current.projection = FALSE)

get_projection(shp)

Arguments

shp
shape object, which is one of
  • "1)"
SpatialPolygons(DataFrame) "2)"

Value

  • set_projection returns a (transformed) shape object with updated projection information. get_projection returns the PROJ.4 character string of shp.

item

  • projection
  • current.projection
  • transform
  • overwrite.current.projection

code

FALSE

describe

  • "longlat"Not really a projection, but a plot of the longitude-latitude coordinates (WGS84 datum).
  • "wintri"Winkel Tripel (1921). Popular projection that is useful in world maps. It is the standard of world maps made by the National Geographic Society. Type: compromise
  • "robin"Robinson (1963). Another popular projection for world maps. Type: compromise
  • "eck4"Eckert IV (1906). Projection useful for world maps. Area sizes are preserved, which makes it particularly useful for truthful choropleths. Type: equal-area
  • "hd"Hobo-Dyer (2002). Another projection useful for world maps in which area sizes are preserved. Type: equal-area
  • "gall"Gall (Peters) (1855). Another projection useful for world maps in which area sizes are preserved. Type: equal-area
  • "merc"Mercator (1569). Projection in which shapes are locally preserved. However, areas close to the poles are inflated. Google Maps uses a close variant of the Mercator. Type: conformal
  • "utmXX(s)"Universal Transverse Mercator. Set of 60 projections where each projection is a traverse mercator optimized for a 6 degree longitude range. These ranges are called UTM zones. Zone 01 covers -180 to -174 degrees (West) and zone 60 174 to 180 east. Replace XX in the character string with the zone number. For southern hemisphere, add "s". So, for instance, the Netherlands is "utm31" and New Zealand is "utm59s"
  • "mill"Miller (1942). Projetion based on Mercator, in which poles are displayed. Type: compromise
  • "eqc0"Equirectangular (120). Projection in which distances along meridians are conserved. The equator is the standard parallel. Also known as Plate Carr'ee. Type: equidistant
  • "eqc30"Equirectangular (120). Projection in which distances along meridians are conserved. The latitude of 30 is the standard parallel. Type: equidistant
  • "eqc45"Equirectangular (120). Projection in which distances along meridians are conserved. The latitude of 45 is the standard parallel. Also known as Gall isographic. Type: equidistant
  • "rd"Rijksdriehoekstelsel. Triangulation coordinate system used in the Netherlands.

url

  • http://en.wikipedia.org/wiki/List_of_map_projections
  • http://trac.osgeo.org/proj/