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rggplot2ggmap

ggmap, using coord_cartesian pushes all points to the north

As the title says when I add coord_cartesian to my ggmap it moves all of my points up. Here's some data.

pricedata<-structure(list(nodename = c("CIN.WABRIVR.2", "CIN.WHEATCTG1", 
                                       "CONS.ADA", "CONS.ALCONA", "CONS.CADILAC", "CONS.CROTON", "CONS.GAYLORD1", 
                                       "CONS.GRATIOT1", "CONS.GRAYLGY2", "CONS.GRAYLNG", "CONS.HARDY", 
                                       "CONS.HILLMAN", "CONS.HODENPYL", "CONS.HOLL", "CONS.KALK", "CONS.KARN1", 
                                       "CONS.KENCNTY1", "CONS.LANS", "CONS.LUDINGTN1", "CONS.MIPOWER1", 
                                       "CONS.RENAIGEN1", "CONS.STRAITS", "CONS.TUSCOLA1", "CONS.VKLINCOLN", 
                                       "CONS.VKMCBAIN1", "CONS.ZEELAND1A"), 
                          lat = c(39.922328, 39.53, 42.962672, 44.561961, 44.26169, 43.437322, 45.0306, 43.433889, 
                                  43.408056, 44.604921, 43.486618, 45.0688, 44.36286, 42.7925, 44.6889, 43.644996, 
                                  42.949575, 42.719722, 43.8942, 43.9375, 43.1864, 45.766859, 43.525278, 44.68, 44.204, 42.8067), 
                          lon = c(-87.446358, -87.4247, -85.494071, -83.804505, -85.435224, -85.664462, -84.7039, -84.4975, -84.462222, 
                                  -84.690578, -85.629866, -83.8932, -85.819968, -86.092222, -85.2019, -83.840074, -85.693209, -84.551667, 
                                  -86.4447, -86.425, -84.8429, -84.756601, -83.65, -83.4167, -85.2206, -86.0558), 
                          price = c(30.3, 32.08, 36.71, 35.78, 36.12, 36.33, 35.58, 35.16, 36.12, 36.12, 35.9, 35.8, 36.05, 36.38, 
                                    35.98, 23.18, 36.06, 34.55, 34.87, 34.6, 34.6, 38.49, 34.23, 35.64, 35.43, 36.33), 
                          pricecut = structure(c(7L, 7L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 
                                                 8L, 8L, 5L, 8L, 8L, 8L, 8L, 8L, 9L, 8L, 8L, 8L, 8L), 
                         .Label = c("(-10,0]", "(0,6]", "(6,14]", "(14,20]", "(20,26]", "(26,30]", "(30,34]", 
                                    "(34,38]", "(38,42]", "(42,46]", "(46,50]", "(50,56]", "(56,62]", "(62,68]", 
                                    "(68,76]", "(76,82]", "(82,90]", "(90,100]", "(100,115]", "(115,125]", "(125,150]", 
                                    "(150,200]", "(200,250]", "(250,300]", "(300,400]", "(400,500]", 
                                    "(500,600]", "(600,800]", "(800,1e+03]"), 
                         class = c("ordered", "factor"))), .Names = c("nodename", "lat", "lon", "price", "pricecut"), row.names = 75:100, class = "data.frame")

Here's my code plus the result

m<-get_map(location=c(lon=-89.6,lat=41.8),zoom=5)
base<-ggmap(m,extent='device') 
base+geom_point(aes(x=lon,y=lat, colour=pricecut), size=6, alpha=.7, data=pricedata)

enter image description here

That is the result I expect

However, when I add coord_cartesian things get strange

base+geom_point(aes(x=lon,y=lat, colour=pricecut), size=6, alpha=.7, data=pricedata)+coord_cartesian(xlim=c(-95,-80), ylim=c(38,50))

enter image description here

Solution

  • Instead of using coord_cartesian you can probably better set the limits with scale_x_continuous and scale_y_continuous as follows:

    ggmap(m) +
  geom_point(aes(x=lon,y=lat, colour=pricecut), size=6, alpha=.7, data=pricedata) +
  scale_x_continuous(limits = c(-95, -80), expand = c(0, 0)) +
  scale_y_continuous(limits = c(38, 50), expand = c(0, 0))

    which gives the following map:

    enter image description here

    Note: I omitted extent='device' from the ggmap call so you can see what the boundaries are in this plot.

    As with regard to the effect of using coord_cartesian, it seems that coord_cartesian somehow messes with the ratios of the map. Let's start with just the map:

    ggmap(m)

    gives:

    enter image description here

    When you slice this map with scale_y_continuous:

    ggmap(m) +
  geom_blank() +
  scale_y_continuous(limits = c(38, 50), expand = c(0, 0))

    you get:

    enter image description here

    However when doing a similar slice with coord_cartesian:

    ggmap(m) +
  geom_blank() +
  coord_cartesian(ylim=c(38,50))

    you get:

    enter image description here

    As you can see, the map gets stretched horizontally while at the same time maintaining the same height. This causes the map to shift vertically. When using scale_y_continuous the map keeps the correct ratio. It's therefore not the points that get shifted upwards, but the map that gets shifted downwards.