Fig. 1
![Fig. 1](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs12913-018-3225-4/MediaObjects/12913_2018_3225_Fig1_HTML.png)
Map of Nigeria showing boundaries of six geopolitical zones, 36 states and Federal Capital Territory (FCT-Abuja). Shapefile is obtained from gadm.org. The 2018 GADM license allows data re-use for academic and other non-commercial purposes (https://gadm.org/license.html, last accessed: 14th May 2018)