Roth Robert E, Woodruff Andrew W, Johnson Zachary F
GeoVISTA Center, Penn State University, 302 Walker Building, University Park, PA 16802.
Cartogr J. 2010 May 1;47(2):130-140. doi: 10.1179/000870409X12488753453372.
The cartogram, or value-by-area map, is a popular technique for cartographically representing social data. Such maps visually equalize a basemap prior to mapping a social variable by adjusting the size of each enumeration unit by a second, related variable. However, to scale the basemap units according to an equalizing variable, cartograms must distort the shape and/or topology of the original geography. Such compromises reduce the effectiveness of the visualization for elemental and general map-reading tasks. Here we describe a new kind of representation, termed a value-by-alpha map, which visually equalizes the basemap by adjusting the alpha channel, rather than the size, of each enumeration unit. Although not without its own limitations, the value-by-alpha map is able to circumvent the compromise inherent to the cartogram form, perfectly equalizing the basemap while preserving both shape and topology.
统计地图，即面积值地图，是一种用于以地图形式呈现社会数据的常用技术。此类地图在通过第二个相关变量调整每个枚举单元的大小来映射社会变量之前，会对基础地图进行视觉上的均衡处理。然而，为了根据均衡变量对基础地图单元进行缩放，统计地图必须扭曲原始地理区域的形状和/或拓扑结构。这种折衷降低了可视化在基本和一般地图阅读任务中的有效性。在此，我们描述一种新的表示形式，称为透明度值地图，它通过调整每个枚举单元的透明度通道而非大小来对基础地图进行视觉上的均衡处理。尽管透明度值地图也有其自身的局限性，但它能够规避统计地图形式固有的折衷问题，在保留形状和拓扑结构的同时完美地均衡基础地图。
