[R] Labelling a fortified GADM map plotted with ggplot and geom_map

Kenneth Dyson kenneth at kidscodejeunesse.org
Mon Mar 19 14:18:57 CET 2018

I am having trouble getting data labels to display over the provinces in a GADM map of Canada.
Specifically, I need the variable "Number" from the data set "by_province", grouped by "region", to appear on the corresponding regions of the map.

The data set "by_province" looks like this:
long      lat          order  hole piece                   region                     group     Number
-110.37074 60.00006       1 FALSE     1                   Alberta                    Alberta.1    132
-110.36250 60.00006       2 FALSE     1                   Alberta                    Alberta.1    132
-110.35103 60.00006       3 FALSE     1                   Alberta                    Alberta.1    132
and the data set "tract" is the map data without the "Number" variable.
I looked into working this out from by researching the geom_map function here: http://ggplot2.tidyverse.org/reference/geom_map.html
my code looks like this:
# get the raw map data
can_map <- getData('GADM', country = "CAN", level = 1) # download map level with provinces
tract <- fortify(can_map, region = "NAME_1") # transforms data from shapefiles into a dataframe that ggplot can understand, from http://www.kevjohnson.org/making-maps-in-r/

# create subsets of the kcj data if needed, for example by year
kids_data_2017 <- subset(kids_data, year == 2017) # data for the year 2017
kids_data_2018 <- subset(kids_data, year == 2018) # data for the year 2018

# extract the needed data
kids_province_data <- data.table::data.table(kids_data_2017$Province_Territory__c, kids_data_2017$Number_of_kids__c)
names(kids_province_data)[1] <- "Province"
names(kids_province_data)[2] <- "Number"

# sum the data by province
kids_province_sums <- aggregate(.~Province, data = kids_province_data, sum)

# join the data to the map
names(tract)[6] <- "region"
names(kids_province_sums)[1] <- "region"
by_province <- left_join(tract, kids_province_sums)

# create the data map
kids_map <- ggplot(by_province, aes(map_id = region)) +              #plots the map in by_province separating by region
           geom_map(aes(fill = Number),                             #generates aestheticsa for the plot
                    map = tract,                                        #takes the data from tract
                    color = "#ffffff",                                  #makes the color of the borders between regions white
                    size = 0.15) +                                      #sets the thickness of the boarder lines
           coord_map("polyconic") +                                 #sets the coordinates to polyconic (rounded lat and long)
           scale_fill_gradient(name = "Children Reached",           #sets the gradient of the value scale: names the scale
                               low = grey_2,                            #color of the low end
                               high = orange_1) +                       #color of the high end
           expand_limits(x = tract$long,                            #ensure limits include all values for all plots
                         y = tract$lat) +
           labs(x = NULL,                                           #add labels, no x title
                y = NULL,                                               #no y title
                title = "Number of Children Reached by Province",       #map title
                subtitle = "2017") +                                    #map subtitle
           geom_text(data = by_province,                            #add a text layer
                     aes(long,                                          #aethetics for the text, x axis
                         lat,                                               #y axis
                         label = Number,                                    #the value to display
                         size=3)) +                                         #size of the text
           theme(axis.ticks = element_blank(),                      #theme of the graph, no axis ticks
                 axis.text = element_blank(),                           #no axis text
                 panel.background = element_blank(),                    #blank background
                 panel.border = element_blank())                        #blank border

# save as png
ggsave(kids_map, file = "kids_map.png", width = 6, height = 4.5, type = "cairo-png”)
I have asked this question on stack overflow, and was refered to this answer:

The solution there did not fix my problem, though it did get me closer.
The solution on that post is using a single vector of labels.

My post on stackoverflow has images of my output:

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