Create a ggplot2 basemap for plotting variables

Source: R/basemap.R

Creates a ggplot2 basemap for further plotting of variables.

basemap(
  type = "panarctic",
  limits = NULL,
  limits.lon = NULL,
  limits.lat = NULL,
  round.lon = FALSE,
  n.lon.grid = 3,
  lon.interval = NULL,
  round.lat = FALSE,
  n.lat.grid = 3,
  lat.interval = NULL,
  keep.glaciers = TRUE,
  legends = TRUE,
  legend.position = "right",
  bathymetry = FALSE,
  bathy.style = "poly_blues",
  bathy.detailed = FALSE,
  bathy.border.col = NA,
  bathy.size = 0.1,
  land.col = "grey60",
  land.border.col = "black",
  land.size = 0.1,
  gla.col = "grey95",
  gla.border.col = "black",
  gla.size = 0.1,
  grid.col = "grey70",
  grid.size = 0.1,
  currents = FALSE,
  arc.col = "blue",
  atl.col = "#BB1512",
  current.size = 0.5,
  current.alpha = 1,
  label.print = TRUE,
  label.offset = 1.05,
  label.font = 8,
  base_size = 11,
  plot = TRUE
)

Arguments

type

Type of map area. Options: "panarctic", "barentssea", "svalbard", "mosj", "kongsfjorden", "kongsfjordbotn", "kronebreen", or "rijpfjorden". See details.
limits

Map limits. One of the following options:

  • numeric vector of length 4: The first element defines the minimum longitude, the second element the maximum longitude, the third element the minimum latitude and the fourth element the maximum latitude of the bounding box. The coordinates have to be given as decimal degrees for Svalbard and Barents Sea maps and as UTM coordinates for pan-Arctic maps. See "Examples", map_projection and transform_coord how to find these coordinates.

  • character vector of length 3: the first element gives the object name of the data frame containing data to which the map should be limited, the second argument gives the column name of longitude data and the third argument the column name of latitude data. The map will be limited using rounded minimum and maximum floor and ceiling values for longitude and latitude. Use the limits.lon and limits.lat arguments to define the accuracy of rounding.

  • single integer between 40 and 88: works only for the "panarctic" map type. Round map will be produced with a limit at the given decimal degree latitude.
limits.lon, limits.lat

Numeric. The level of rounding for longitude and latitude, respectively, when using automatic limits (character vector in limits argument). If NULL, sensible default values are used.
round.lon, round.lat

Numeric value specifying the level of rounding to be used to plot longitude and latitude grid lines. Override n.lon.grid or n.lat.grid
n.lon.grid, n.lat.grid

Numeric value specifying the number of longitude and latitude grid lines, respectively. Alternatively use round.lon and round.lat
lon.interval, lat.interval

Numeric value specifying the interval of longitude and latitude grids for the "panarctic" map type. NULL finds reasonable defaults depending on limits.
keep.glaciers

Logical indicating whether glaciers should be kept for the Svalbard maps. Setting this to FALSE speeds up map plotting by a few seconds.
legends

Logical indicating whether legends for bathymetry and/or ocean currents should be shown. Can be a single logical applying to all legends or a logical vector of length 2. The first element applies for bathymetry and the second for ocean currents.
legend.position

Position for ggplot2 legend. See the argument with the same name in theme.
bathymetry

Logical indicating whether bathymetry should be added to the map. Relatively slow.
bathy.style

Character defining the style for bathymetry contours. Alternatives:

  • "poly_blues" plots polygons filled with different shades of blue.

  • "poly_greys" plots polygons filled with different shades of grey.

  • "contour_blues" contour lines with different shades of blue.

  • "contour_grey" plots grey contour lines.
bathy.detailed

Logical indicating whether detailed bathymetry shapefiles should be used. Works for Svalbard maps only (see Source). Very slow due to the large file size. Use for limited areas, such as fjords, only.
land.col, gla.col, grid.col

Character code specifying the color of land, glaciers and grid lines, respectively. Use NA to remove the grid lines.
land.border.col, gla.border.col, bathy.border.col

Character code specifying the color of the border line for land, glacier, and bathymetry shapes.
land.size, gla.size, bathy.size, grid.size

Numeric value specifying the width of the border line for land and glacier shapes as well as the width of the grid lines, respectively. See details for explanation about line widths.
currents

logical indicating whether Arctic and Atlantic ocean currents for the Barents Sea should be plotted. See details.
arc.col, atl.col

Character code specifying the color for Arctic and Atlantic current arrows.
current.size

Either a numeric value specifying the width of ocean current arrows or "scaled" for ocean currents that are approximately scaled to their magnitude.
current.alpha

Value between 0 and 1 defining the transparency of current arrows.
label.print

Logical indicating whether labels should be printed for polar stereographic maps.
label.offset

Offset between the round polar stereographic maps and longitude labels. Optimized for a pdf output. Use 1.1 for larger size figures.
label.font

Numeric value specifying the font size for labels in polar stereographic maps. Note that this value defines the actual font size in points, not the ggplot2 font size.
base_size

Base size parameter for ggplot. See theme_bw.
plot

logical indicting whether a ggplot should be returned. If FALSE underlying data for the basemap will be returned allowing further customization.

Source

Value

If plot = TRUE, returns a ggplot2 map, which can be assigned to an object and modified as any ggplot object. Otherwise returns a list of basemap data.

Details

The function uses ggplot2 and shapefiles to plot maps of Svalbard and other polar regions. The Svalbard shapefiles are detailed and glaciers varyingly up-to-date (2017 for Kongsfjorden; mostly 2015 for the rest, but not systematically checked) detailed The map type is defined using the type argument and map limits can be controlled with the limits argument. Currently implemented map types:

  • "panarctic". A polar stereographic map of the Arctic with a limit at 40 degrees North. This map type can be used to plot maps of any location north of 40 degrees latitude.

  • "barentssea". A 1:10 000 000 map of the Barents Sea.

  • "svalbard". Detailed 1:250 000 map of Svalbard land and glaciers. This option is slow (approx. 25 seconds) due to the large file size.

  • "mosj" shows Kongsfjoden and Fram Strait as sampled during Norwegian Polar Institute's (NPI) MOSJ campaigns. Some glaciers can be older than 2015.

  • "kongsfjorden" shows Kongsfjorden and parts of Prins Karls Forland. Glaciers are from 2015 to 2017.

  • "kongsfjordbotn" shows Kongsvegen, Kronebreen, Kongsbreen and Conwaybreen. Glaciers are from July 2017.

  • "kronebreen" shows mostly Kronebreen and Kongsvegen. Glacier fronts are from July 2017.

  • "rijpfjorden" shows NPI's Rijpfjorden to the Arctic Ocean transect. The glaciers have not been updated and might be old.

Svalbard and Barents Sea maps use the "+init=epsg:32633" UTM projection. The polar stereographic maps use "+proj=stere +lat_0=90 +lat_ts=71 +lon_0=0 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs +ellps=WGS84 +towgs84=0,0,0" projection. The "mosj", "kongsfjorden", "kongsfjordbotn", "kronebreen", and "rijpfjorden" maps use a subset of the Svalbard shape files and are faster to plot due to a smaller file size. These alternatives give convenient limits for certain regions the main author has worked with recently. New map types can be implemented relatively easily, but require digging into the source code.

Line width (size) aesthetics in ggplot2 generates approximately 2.13 wider lines measured in pt than the given values. If you want a specific line width in pt, multiply it by 1/2.13. Internal functions LS and FS are available to convert line and font sizes in points to ggplot2 equivalents.

Ocean currents for the Barents Sea are implemented, but not peer-reviewed yet. This feature will be improved in the future versions of the package.

See also

ggplot2 theme_map

Examples

basemap() ## Plots Kongsfjorden

## Maps work as normal ggplot2 objects:

data(chlorophyll)
p <- basemap("mosj")
p + geom_point(data = chlorophyll, aes(x = lon.utm, y = lat.utm,
size = Chla, color = Chla), shape = 1)

## Limiting maps can be done using the limits argument:
basemap("kongsfjordbotn", limits = c(12.2,12.65,78.95,79.00))

## Automatic limits find the boundary of data
basemap("barentssea", limits = c("chlorophyll", "lon", "lat")) +
geom_point(data = chlorophyll, aes(x = lon.utm, y = lat.utm,
size = Chla, color = Chla), shape = 1)

## Svalbard map. Warning: this is SLOW
basemap("svalbard")

## grid.col = NA removes grid lines
basemap("svalbard", grid.col = NA, limits = c(10, 28, 79.5, 83))

## Use round.lat and n.lon.grid arguments
## to control grid lines
basemap("svalbard", limits = c(3,24,78.5,82), round.lat = 1,
n.lon.grid = 4)

## Modify axis labels
basemap("barentssea") + xlab("Lat")
basemap("barentssea") + labs(x = NULL, y = NULL) # remove axis labs
basemap("barentssea") + theme(axis.title = element_blank()) # another way

## Barents Sea
basemap("barentssea")

## Barents Sea map also prints mainland Norway,
## but the projection is not optimal.
basemap("barentssea", limits = c(12, 24, 68, 71))

## Polar stereographic pan-Arctic maps
basemap("panarctic", limits = 50)

## To find UTM coordinates to limit a pan-Arctic map:
basemap("panarctic") + theme_bw()
basemap("panarctic", limits = c(2.5e4, -2.5e6, 2e6, -2.5e5))

## Bathymetry can be added using the bathymetry argument
basemap("panarctic", limits = 50, bathymetry = TRUE)

## Detailed bathymetry is available for some
## Svalbard fjords
basemap("kongsfjorden", bathymetry = TRUE, bathy.detailed = TRUE)

## Ocean currents for the Barents Sea
basemap("barentssea", bathymetry = TRUE, currents = TRUE)
basemap("barentssea", bathymetry = TRUE, currents = TRUE,
current.size = "scaled", legends = c(FALSE, TRUE))