read_shape: Read shape file

Description

Read an ESRI shape file. Optionally, set the current projection if it is missing.

Usage

read_shape(file, current.projection = NULL, ...)

Arguments

file

a shape file name (including directory)

current.projection

the current projection of the shape object, if it is missing in the shape file. It should be either a PROJ.4 character string (see http://trac.osgeo.org/proj/), of one of the following shortcuts:

"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.

See http://en.wikipedia.org/wiki/List_of_map_projections for a overview of projections. Use set_projection to reproject the shape object.

...

other parameters, such as stringsAsFactors, are passed on to readOGR

Value

shape object

Details

This function is a convenient wrapper of rgdal's readOGR. It is possible to set the current projection, if it is undefined in the shape file. If a reprojection is required, use set_projection.

For the Netherlands: often, the Dutch Rijksdriehoekstelsel (Dutch National Grid) projection is provided in the shape file without proper datum shift parameters to wgs84. This functions automatically adds these parameters. See http://www.qgis.nl/2011/12/05/epsg28992-of-rijksdriehoekstelsel-verschuiving/ (in Dutch) for details.