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

[Bert Gunter]

The r-sig-geo list,

https://stat.ethz.ch/mailman/listinfo/r-sig-geo

is often a better place to post such geographically related queries.

Cheers,
Bert





Bert Gunter

"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )

On Mon, Mar 19, 2018 at 6:18 AM, Kenneth Dyson <kenneth at kidscodejeunesse.org
> wrote:

> 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:
>
> https://stackoverflow.com/questions/9441436/ggplot-centered-names-on-a-map
> 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:
> https://stackoverflow.com/questions/49118323/labelling-
> a-map-plotted-with-geom-map
>
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>
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