If you go to any good beauty parlour they tend to give free skin mappings. So you go for a consultation and they tell you whether your skin is dry, oily etc and in which areas, and they'll also recommend products for you to use :)
Okay I found this. Dermalogica is a really well reputed skin-care brand and here is their online skin mapping service. Goo luck. http://funadvice.com/r/bg1k63p0kcd :)
Is there anyway I can just find out at home?