what is the problem with my hair? (pictures)

[YAZAN]

(sorry for my bad english)hi,i have a question about my hair..i didn't have this problem in 2015, but after that in 2016 i used to wear hat everyday and everytime i want to go outside also i let my hair to grow more (7cm/2.7inch).. after that in the last of 2016 and the beginnig of 2017 i convinced my self to cut all my hair, so when i cut it i realised the empty area in my crown .. so what is that? is that a thinning problem or a hair loss? is it gonna extand? and what is the cure ?