World city populations 1950–2030: Proportional circle time series map
该研究用重叠的比例圆图层在一张图上展示全球城市人口的时间序列数据，直观呈现城市人口规模和增长，对地理信息可视化领域有参考价值。
Visualising change over time is a common cartographic task, with solutions ranging from mapping change variables to multiple map frames, interactive maps and animations.In this graphic a global time-series of city population data is mapped through a series of overlapping proportional circle layers representing different points in time.This technique allows spatial time series data to be perceived in a single image, communicating both magnitude and growth in city populations (Figure 1).While this is not a new cartographic technique (see for example Burdett et al., 2011), but is not often used and is relevant for visualising global dynamic datasets.