Setting map borders in ggplot2 with Mercator projection

Question

Very related to this issue . I am trying to speak some regions of the world, now using the Mercator projection, but I continue to encounter problems when adding the limitations of x and y:

ggplot(world, mapping = aes(x = long, y = lat, group = group)) +
  geom_polygon(fill = "black", colour = "black") +
  coord_map(projection = "mercator", xlim = c(-125, -30), ylim = c(-60, 35))

Obviously, this is not great. When I use coord_cartesian(as suggested here ) to set limits, I lose the Mercator projection:

ggplot(world, mapping = aes(x = long, y = lat, group = group)) +
  geom_polygon(fill = "black", colour = "black") +
  coord_map(projection = "mercator") +
  coord_cartesian(xlim = c(-125, -30), ylim = c(-60, 35))

When I use lims, I get what I want for Latin America:

ggplot(world, mapping = aes(x = long, y = lat, group = group)) +
  geom_polygon(fill = "black", colour = "black") +
  coord_map(projection = "mercator") +
  lims(x = c(-125, -30), y = c(-60, 35))

The problem is that this approach does not always work, for example, for Africa or Asia. I start crazy behavior towards the border of the plot:

ggplot(world, mapping = aes(x = long, y = lat, group = group)) +
  geom_polygon(fill = "black", colour = "black") +
  coord_map(projection = "mercator") +
  lims(x = c(-20, 45), y = c(-50, 40))
  # lims(x = c(40, 150), y = c(-10, 55))

Answer 1

lat/lon "" - ( epsg 3857, "google" ), "" .

, latlon wgs84 (epsg 4326), :

worldmerc <-  SpatialPointsDataFrame(coords = data_frame(x = world$long, y = world$lat), 
                                data = world, proj4string = CRS("+proj=longlat +datum=WGS84")) %>%
         subset((lat < 90 & lat > -90)) %>%   # needed because transform not defined at the poles !!!!
         spTransform(CRS("+init=epsg:3857")) 
worldmerc  <-  mutate(worldmerc@data, longmerc = coordinates(worldmerc)[,1], latmerc = coordinates(worldmerc)[,2])

( coord_fixed !:

ggplot(worldmerc, mapping = aes(x = longmerc, y = latmerc, group = group)) +
  geom_polygon(fill = "black", colour = "black") +coord_fixed()

, "map", lat long, :

#For South America
xlim = c(-125, -30)
ylim = c(-60, 35)

lims = SpatialPoints(coords = data_frame(x = xlim, y = ylim), proj4string = CRS("+proj=longlat +datum=WGS84"))%>%
  spTransform(CRS("+init=epsg:3857"))

ggplot(worldmerc, mapping = aes(x = longmerc, y = latmerc, group = group)) +
  geom_polygon(fill = "black", colour = "black")+
  coord_fixed(xlim = coordinates(lims)[,1], ylim = coordinates(lims)[,2])

#for africa
xlim = c(-20,45)
ylim = c(-50,40)

lims = SpatialPoints(coords = data_frame(x = xlim, y = ylim), proj4string = CRS("+proj=longlat +datum=WGS84"))%>%
       spTransform(CRS("+init=epsg:3857"))

ggplot(worldmerc, mapping = aes(x = longmerc, y = latmerc, group = group)) +
  geom_polygon(fill = "black", colour = "black")+
  coord_fixed(xlim = coordinates(lims)[,1], ylim = coordinates(lims)[,2])

, "" .

, , , , , , , "lat/lon" . , :

library(magrittr)
xlim = c(-125, -30)
ylim = c(-60, 35)

# Get the coordinates of the limits in mercator projection
lims = SpatialPoints(coords = data_frame(x = xlim, y = ylim), 
                     proj4string = CRS("+proj=longlat +datum=WGS84"))%>%
       spTransform(CRS("+init=epsg:3857"))

# Create regular "grids" of latlon coordinates and find points 
# within xlim/ylim - will be our labels

majgrid_wid_lat = 20
majgrid_wid_lon = 30

majbreaks_lon = data_frame(x=seq(-180,  180, majgrid_wid_lon)) %>% 
                filter(x >= xlim[1] & x <= xlim[2]) %>% 
                as.data.frame()
majbreaks_lat = data_frame(x=seq(-90,   90, majgrid_wid_lat)) %>%
                filter(x >= ylim[1] & x <= ylim[2]) %>% 
                as.data.frame()

#Find corresponding mercator coordinates

mercbreaks_lat = SpatialPoints(coords = expand.grid(x = majbreaks_lon$x, y = majbreaks_lat$x), proj4string = CRS("+init=epsg:4326"))%>%
  spTransform(CRS("+init=epsg:3857")) %>% coordinates() %>% extract(,2) %>% unique() 
mercbreaks_lon = SpatialPoints(coords = expand.grid(x = majbreaks_lon$x, y = majbreaks_lat$x), proj4string = CRS("+init=epsg:4326"))%>%
  spTransform(CRS("+init=epsg:3857")) %>% coordinates()  %>% extract(,1) %>% unique()

# Plot using mercator coordinates, but latlon labels

ggplot(worldmerc, mapping = aes(x = longmerc, y = latmerc, group = group)) +
  geom_polygon(fill = "black", colour = "black") +
  coord_fixed(xlim = coordinates(lims)[,1], ylim = coordinates(lims)[,2])+
  scale_x_continuous("lon", breaks = mercbreaks_lon, labels = signif(majbreaks_lon$x, 2)) + 
  scale_y_continuous("lat", breaks = mercbreaks_lat, labels = signif(majbreaks_lat$x,2))+theme_bw() 

:

, , .

HTH,