Terrain Basemap for thematic mapping

Thematic maps are single-topics maps that focus on the spatial variability of a specific distribution. At USAID’s Office of HIV/AIDs, we’ve used thematic maps to visualize the spatial distibution of HIV/AIDs Programs’ key indicators at the PSNU level. ART Saturation of Nigeria at the psnu level is a good example of one of these thematic maps. In most countries, HIV/AIDs programs are implemented only in specific districts by USAID, and creating such a thematic map usually leads to having to deal with empty states. To compensate for the non-presence in some of these districts, we used terrain rasterlayer as a basemap. These basemaps are generated in way to that the hillshape is used as a beautifier of the map.

Below are how we go about creating these basemaps

library(dplyr)         # General data munging and visualisation
library(ggplot2)       # General plotting
library(gisr)          # OHA/SI in house package used to create these basemap
library(sf)            # Spatial data management
library(glitr)         # OHA/SI in house package used to help standardize viz

We will be using Nigeria as our country of focus. Let’s extract the country boundary and the states boundaries.

countryname <- "Nigeria"

adm0 <- gisr::get_admin0(countries = countryname) %>% 
  dplyr::select(admin)

adm1 <- gisr::get_admin1(countries = countryname) %>% 
  dplyr::select(name)

What does the country map look like?

adm0 %>% gisr::gview()

What does the states map look like?

adm1 %>% 
  gisr::gview() + 
  ggplot2::geom_sf_text(data = adm1, ggplot2::aes(label = name), size = 3)

Let’s create a basemap for Nigeria.

For this, We will need to downlaod the raster file into si_path("path_raster")

This option uses rnaturalearth to extract admin0 and admin1 boundaries as sf objects.

terrain_map(countries = countryname, 
            mask = TRUE,
            glamr::si_path("path_raster"))

We could also provide you own admins boundaries. This is a classic case where official country names don’t match with rnaturalearth names. Tanzania is good example where the country name is United Republic of Tanzania.

terrain_map(countries = adm0,
            adm0 = adm0,
            adm1 = adm1,
            terr = glamr::si_path("path_raster"))

We could also decide to use only the country boundaries

terrain_map(countries = adm0,
            adm0 = adm0,
            terr = glamr::si_path("path_raster"))

It’s also possible to add neighbor countries to your basemap. See below.

ras <- glamr::si_path("path_raster")

terrain_map(countries = adm0,
            adm0 = adm0,
            adm1 = adm1,
            add_neighbors = TRUE,
            add_labels = TRUE,
            terr = ras)