Q:

How to highlight locations on a tmap in R?

I am trying to use tm_text to add text to define locations on a map using the tmap package in R.
This is the code i have used to produce my map:
library(tmap)
library(spData)

     tm_shape(nz) +
          tm_fill("Population") +
          tm_borders() +
          tm_layout(basemaps = leaflet::providers$Esri.WorldTopoMap)

I can not find another base map which would highlight the locations on the map that I am interested in so I was wondering whether there is a way I can over lay text into certain areas?
For example in the image below I would like to add text to highlight central hawks bay district and palmerton North.

A:

To add text to a tmap map via the tm_text() call you need two things - a label, and a location.
With a little help of google maps I have found coordinates for Palmerston North and Central Hawke's Bay (never heard of either before :) and I propose the following solution:
library(tmap)
library(spData)
library(sf)

points <- data.frame(name = c("Central Hawke's Bay", "Palmerston North"),
                     x = c(176.474193, 175.611667),
                     y = c(-39.922303, -40.355),
                     stringsAsFactors = F)

points <- st_as_sf(points, coords = c("x", "y"), crs = 4326)

tmap_mode("view")

tm_shape(nz) +
  tm_fill("Population") +
  tm_borders() +
  tm_shape(points) + tm_text("name") +
  tm_basemap(leaflet::providers$Esri.WorldTopoMap)

I have included a library call to {sf} to facilitate conversion of coordinates as number to spatial data frame. I have also slightly amended your {tmap} call to suit current tmap best practices.

