I am trying to give border to total of 2 geom tiles in ggplot2 with different colors. i have 5 cities on y axis and dates as in format “mmm-YY”on x axis from Mar-20 till Nov-20. Out of 5 cities, i want to give black color border to Aug-2020 tile of city-1 and red color border to Jul-2020 of city-2. so far i tried to add border to one of the cities i.e. city-1.