Maps

tda_map draws spatial objects in a geographical coordinate system – a projection, rather than the plain x and y of plot(). TDA builds that system with psetupg and then draws with sdpmap; graticule adds meridians and parallels with sdpgrat, and points adds coordinates given directly with sdpgeo.

Usage

tda_map(
  s,
  view,
  region,
  projection = 10,
  width = 150,
  graticule = list(),
  points = NULL,
  symbol = 1,
  newpage = TRUE,
  ...
)

Arguments

s

a tda_spatial structure.

view

centre of the projection, as longitude and latitude.

region

half-width and half-height of the mapped area, in degrees.

projection

10 cylindrical equidistant, 11 cylindrical equal-area, 12 Mercator, 20 azimuthal orthographic. For projection 20 the longitude half-width is limited to 90 degrees, and the whole region rectangle must fit on the projection disc, so both halves of region need sin(lon)^2 + sin(lat)^2 <= 1 at the view latitude.

width

width of the plot in mm.

graticule

a list of options for the meridians and parallels, or NULL for none. lon and lat take TDA's sequence notation, "-84(2)-76" meaning every 2 degrees from -84 to -76.

points

a data frame of lon and lat to mark, or NULL.

symbol

marker symbol for points; TDA's s=, which cannot be spelled that way here because s is the structure. 4 is an open circle, 5 a filled one, 8 a square, 15 a diamond.

newpage

start a new grid page.

...

further options for sdpmap.

Value

The map, drawn; the session is returned invisibly.

Details

region is required and has no default: it is the half-width and half-height of the mapped area in degrees, measured from view. So view = c(-80, 35), region = c(6, 3) maps 6 degrees of longitude and 3 of latitude either side of that point.

See also

Other spatial analysis: plot.tda_spatial(), tda_polygons(), tda_read_dbf(), tda_read_shapefile(), tda_read_spatial, tda_sd(), tda_sd_analyses, tda_sd_ps3(), tda_spatial()

Examples

if (requireNamespace("sf", quietly = TRUE)) {
  nc <- tda_read_shapefile(system.file("shape/nc.shp", package = "sf"))
  tda_map(nc, view = c(-80, 35), region = c(6, 3),
          graticule = list(lon = "-84(2)-76", lat = "34(1)37",
                           fsx = 2, fsy = 2))
}