Primarily there are two aspects : 1 ) the calculation model of the value of land classifying units - - model of time distance attenuation . in the calculation model of the value of land classifying units , author brings forward the model of time distance attenuation . in this model adopting the network analysis , and by establishing the road network , and proceeding path analysis , computing the time distance , then proceed the exponential attenuation or straight line attenuation on time distance , get the value of influence factor of the land classification unit