We include a reference here to a very useful article published in the Washington Post by Tomás Dosek and Martiza Paredes on the background to the second round. It contains particularly useful graphics on the geography of support for Keiko Fujimori, Pedro Pablo Kuczynski and Verónika Mendoza from the first round, as well as the socio-economic status of their respective voters.
https://www.washingtonpost.com/news/monkey-cage/wp/2016/06/03/peru-might-elect-an-authoritarian-president-these-four-maps-tell-you-whos-voting-how-and-why/