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Create basemapData object for basemap plotting

Source: R/basemap_data.R
basemap_data.Rd

Internal function to create a basemapData object for basemap

Usage

basemap_data(
  limits = NULL,
  data = NULL,
  shapefiles = NULL,
  crs = NULL,
  bathymetry = FALSE,
  bathy.type = NULL,
  downsample = 0,
  glaciers = FALSE,
  lon.interval = NULL,
  lat.interval = NULL,
  expand.factor = 1.1,
  rotate = FALSE,
  verbose = FALSE
)

Arguments

limits

Map limits. One of the following:

  • numeric vector of length 4: The first element defines the start longitude, the second element the end longitude (counter-clockwise), the third element the minimum latitude, and the fourth element the maximum latitude of the bounding box. Also accepts sf::st_bbox type named vectors with limits in any order. The coordinates can be given as decimal degrees or coordinate units for shapefiles used by a projected map. Produces a rectangular map. Latitude limits not given in min-max order are automatically ordered to respect this requirement.

  • single integer between 30 and 88 or -88 and -30 produces a polar map for the Arctic or Antarctic, respectively.

Can be omitted if data or shapefiles are defined.

data

A data frame, sp, or sf shape containing longitude and latitude coordinates. If a data frame, the coordinates have to be given in decimal degrees. The limits are extracted from these coordinates and produce a rectangular map. Suited for situations where a certain dataset is plotted on a map. The function attempts to guess the correct columns and it is advised to use intuitive column names for longitude (such as "lon", "long", or "longitude") and latitude ("lat", "latitude") columns. Can be omitted if limits or shapefiles are defined.

shapefiles

Either a list containing shapefile information or a character argument referring to a name of pre-made shapefiles in shapefile_list. This name is partially matched. Can be omitted if limits or data is defined as decimal degrees.

crs

Coordinate reference system (CRS) for the map. If NULL (default), the CRS is selected automatically based on limits, data, or shapefiles. Passed to st_crs. Typically integers giving the EPGS code are the easiest. Cannot be used simultaneously with rotate.

bathymetry

Logical indicating whether bathymetry should be added to the map. Functions together with bathy.style. See Details.

downsample

Integer defining the downsampling rate for raster bathymetries. A value of 0 (default) does not downsample, 1 skips every second row, 2 every second and third. See geom_stars

glaciers

Logical indicating whether glaciers and ice sheets should be added to the map.

lon.interval, lat.interval

Numeric value specifying the interval of longitude and latitude grids. NULL finds reasonable defaults depending on limits.

expand.factor

Expansion factor for map limits. Can be used to zoom in (decrease the value under 1) and out (increase the value over 1) automatically (data) limited maps. Defaults to 1, which means that outermost data points are located at the boundaries of the plotting region.

rotate

Logical indicating whether the projected maps should be rotated to point towards the pole relative to the mid-longitude limit.

verbose

Logical indicating whether information about the projection and guessed column names should be returned as messages. Set to FALSE to make the function silent.

Value

A list of class basemapData containing information required for plotting a basemap.

Details

This is an internal function, which is automatically run by the basemap function. Common users do not need to worry about these details.

See also

basemap

Author

Mikko Vihtakari