7Search.ccgravity model ap human geographygravity model ap human geographygravity model ap human geography definitiongravity model ap human geography examplegravity model ap humangravity model of migration ap human geographygravity model human geographygravity model human geography definitionap human geography modelsgeographic models ap human geographythe gravity model geographyap human geography theories and modelsmodel definition ap human geography