Global Estimated Net Migration Grids By Decade: 1970-2000

The Global Estimated Net Migration by Decade: 1970-2000 data set provides estimates of net migration over the three decades from 1970 to 2000. Because of the lack of globally consistent data on migration, indirect estimation methods were used. The authors relied on a combination of data on spatial population distribution for four time slices (1970, 1980, 1990, and 2000) and subnational rates of natural increase in order to derive estimates of net migration on a 30 arc-second (~1km) grid cell basis. Net migration was estimated by subtracting the population in time period 2 from the population in time period 1, and then subtracting the natural increase (births minus deaths). The residual was considered to be net migration (in-migrants minus out-migrants). The authors ran 13 geospatial net migration estimation models based on outputs from the same number of imputation runs for urban and rural rates of natural increase.This data set represents the average of those runs. These data are reliable at broad scales of analysis (e.g. ecosystems or regions), but are generally not reliable for local level analyses. The data were produced for the United Kingdom Foresight project on Migration and Global Environmental Change.

《1970-2000年十年期全球估算净迁移数据集》（The Global Estimated Net Migration by Decade: 1970-2000）提供了1970至2000年三个十年间的净迁移（net migration）估算值。由于缺乏全球统一的迁移统计数据，本研究采用间接估算方法。研究团队结合1970、1980、1990及2000年四个时间切片的空间人口分布数据，以及分区域自然增长率，以30弧秒（arc-second，约1公里）的网格单元（grid cell）为基础，推导得到净迁移估算值。净迁移的计算方式为：以第二时段人口减去第一时段人口，再减去自然增长人口（出生人口减去死亡人口），所得剩余值即被视为净迁移（即迁入人口减去迁出人口）。研究团队针对城乡自然增长率开展了13次插补运算（imputation run），基于各次运算的输出结果构建了13个地理空间净迁移估算模型，本数据集即为这13次运算结果的平均值。该数据集适用于大尺度分析场景（如生态系统或区域尺度），但通常无法满足局地尺度的分析需求。本数据集由英国移民与全球环境变化远见项目（United Kingdom Foresight project on Migration and Global Environmental Change）编制产出。