07/01/2020
Install from github using devtools:
library(devtools)
install_github('Chrisjb/basemapR')
A lot of credit has to go to Hiroakki Yutani for his blog
post from
which I borrowed a lot of code for the base_map
function. I hope they
don’t mind!
the base_map
function can be added to a ggplot2 call as follows:
library(ggplot2)
library(sf)
library(basemapR)
ggplot() +
base_map(st_bbox(localauth_data), increase_zoom = 2) +
geom_sf(data = localauth_data, fill = NA)
A bounding box created using st_bbox
or the basemapR function
expand_bbox
(see below). The bounding box defines the extents over
which we want the base map to be returned.
This will normally be the largest layer on our map. Sometimes we will have two distinct layers neither of which covers the full extent of the map on their own. For example:
library(dplyr)
library(basemapR)
library(sf)
camden <- localauth_data %>%
filter(Name == 'Camden')
wandsworth <- localauth_data %>%
filter(Name == 'Wandsworth')
ggplot() +
geom_sf(data = camden) +
geom_sf(data = wandsworth)
We need to create a bbox that combines both layers for the base map to cover the full extents of the canvas:
# create bbox polygons for each and union and then convert back to bbox object
my_bbox <- st_bbox(camden) %>%
st_as_sfc() %>%
st_union(st_as_sfc(st_bbox(wandsworth))) %>%
st_bbox()
ggplot() +
base_map(bbox = my_bbox, basemap = 'hydda', increase_zoom = 2) +
geom_sf(data = camden, fill = NA) +
geom_sf(data = wandsworth, fill = NA) +
ggthemes::theme_map()
## attribution: Tiles courtesy of http://openstreetmap.se/ OpenStreetMap Sweden; Map data © <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors
The zoom parameter is calculated automatically. It can be increased by
setting increase_zoom to an integer value. In the first example we set
increase_zoom = 2
. We can play around with this value as per our
desired aesthetic.
Various options for base maps. The attribution for the base layer should be included on the maps and is returned as a message from the function.
dark
attribution: ©
OpenStreetMap
contributors © CARTO
hydda
positron attribution: Tiles courtesy of http://openstreetmap.se/
OpenStreetMap Sweden; Map data ©
OpenStreetMap
contributors
voyager attribution: ©
OpenStreetMap
contributors © CARTO
wikimedia please see attribution details:
https://wikimediafoundation.org/wiki/Maps_Terms_of_Use
mapnik attribution: ©
OpenStreetMap
contributors
If nolabels=TRUE
the function will fetch the basemap without street or
place labels. This option is only available for some basemaps and will
return a message if unavailable.
This function takes in a bbox object and expands it by a set number of
meters in the X
and Y
directions. If we want an asymmetric expansion
(100m to the east but 1km to the west) we can also specify the
parameters X2
and Y2
.
# define a single point
point <- data.frame(x = -0.086543 ,
y= 51.504567) %>%
st_as_sf(coords= c('x','y'), crs = 4326)
# standard bbox for our point
my_bbox_1 <- st_bbox(point)
# expand the bbox by 1000m
my_bbox_2 <- expand_bbox(my_bbox_1, X = 1000, Y = 1000)
We will have to also set the x and y limits ourselves in coord_sf
to
clip the canvas to our basemap:
ggplot() +
base_map(my_bbox_2, increase_zoom = 1, basemap = 'positron')+
geom_sf(data = point) +
coord_sf(xlim = c(my_bbox_2['xmin'], my_bbox_2['xmax']),
ylim = c(my_bbox_2['ymin'],my_bbox_2['ymax']),crs = 4326)
## https://basemaps.cartocdn.com/light_all/14/8187/5448.pnghttps://basemaps.cartocdn.com/light_all/14/8188/5448.pnghttps://basemaps.cartocdn.com/light_all/14/8187/5447.pnghttps://basemaps.cartocdn.com/light_all/14/8188/5447.png
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