The spd model is made by the ins titute of geographical sciences and natural resources research of chinese academy of sciences . it combines social economic factors , such as city and transportation foundational facilities , with nature factors , for example the digital elevation model ( dem ) and net primary productivity ( npp ) of plants to simulate the spatial distribution of population density of china by the advanced grid generation technology 中國模擬人口密度模型是由中國科學(xué)院地理科學(xué)與資源研究所首先提出的,這個模型試圖利用先進的格網(wǎng)生成技術(shù),將城市、交通基礎(chǔ)設(shè)施等社會經(jīng)濟因子和陸地數(shù)字高程( dem ) 、陸地植被凈第一性生產(chǎn)力( npp )等自然因子相結(jié)合,通過模型的反演,模擬某一時期的中國人口密度空間分布狀況。