Dear applicant since you decided to pursue your Bachelor's degree in Mathematics with Physics and Geography as your subject combinations you can go for M.Sc in Mathematics course if you have profound interest in Mathematics or you can for M.Sc courses based on Geography like Geo Informatics or Political Geography courses or you can take up short term courses on Physics too. But out of all definitely M.Sc in Mathematics will be the best option with added advantage for you,

Good luck!!