ggplot: Faceted map with multiple layers

Question

I'm trying to create a faceted map with two layers using ggplot. One is from a data frame containing lat/lon coordinates, created from a CSV:

head(poijoin)

NAME                           LAT       LNG      level1
ATM  Bank Of America ATM @ WHC 38.92825 -77.01517 ShopService                        
ATM  Bank Of America ATM       38.90577 -77.03654 ShopService
ATM  Bank of America           38.91512 -77.02184 ShopService    
ATM  USAA ATM @CVS             38.91343 -77.03590 ShopService
ATM  Bank of America ATM       38.95511 -77.02473 ShopService

The other one is coming from a street network shape file, turned into a dataframe using fortify:

head(streets_df)

        LNG      LAT order piece id group
1 -77.02704 38.90253     1     1  0   0.1
2 -77.02704 38.90303     2     1  0   0.1
3 -77.02704 38.90303     3     1  0   0.1
4 -77.02704 38.90304     4     1  0   0.1
5 -77.02704 38.90326     5     1  0   0.1

Plotting them individually works just fine, so does overlaying them:

ggplot() +
  geom_point(data = poijoin, aes(x = poijoin$LNG, y = poijoin$LAT)) +
  geom_path(data = streets_df, aes(x = LNG, y = LAT, group = group))

(Not very pretty, I know, but I'm trying to stick to the basic parts of the code here.)

I can also facet the points layer without problems:

ggplot() +
  geom_point(data = poijoin, aes(x = poijoin$LNG, y = poijoin$LAT)) +
  facet_wrap(~ poijoin$level1, nrow=3)

However, if I want to add the streets as a base map to each facet, I'm stuck. This:

ggplot() +
  geom_point(data = poijoin, aes(x = poijoin$LNG, y = poijoin$LAT, color = poijoin$level1)) +
  geom_path(data = streets_df, aes(x = LNG, y = LAT, group = group)) +
  facet_wrap(~ poijoin$level1, nrow=3)

Gives me:

Error in `$<-.data.frame`(`*tmp*`, "PANEL", value = c(8L, 8L, 8L, 8L,  : 
  replacement has 20983 rows, data has 200205

I'm sure the error comes up because the two data frames have a different number of elements (20983 points and 200205 streets), but I still don't get what I'm doing wrong. Any pointers appreciated!

See my answer. I'm fairly certain your issue is in ~ poijoin$level1 — hrbrmstr

hrbrmstr hrbrmstr · Accepted Answer · 2017-12-19T17:09:07

Let's make a reproducible example:

library(hrbrthemes)
library(tidyverse)

Get a map:

st_map <- map_data("state")

Make some points with 3 groups:

set.seed(2017-12-19)
data_frame(
  lat = sample(st_map$lat, 30),
  lng = sample(st_map$long, 30),
  level = rep(c("A", "B", "C"), 10)
) -> points_df

ggplot() +
  geom_path(data=st_map, aes(long, lat, group=group), size=0.25) + # basemap
  geom_point(data=points_df, aes(lng, lat, color=level)) +         # add our points layer
  coord_map("polyconic") +                                         # for funsies
  facet_wrap(~level) +                                             # NEVER use a fully qualified column unless you know what you're doing
  labs(x=NULL, y=NULL) +
  theme_ipsum(grid="") +
  theme(axis.text=element_blank()) +
  theme(legend.position="none")

ggplot2 will apply the basemap across facets and then apply the faceting to any other layers with a level category.

ggplot: Faceted map with multiple layers

1 Answers