第七屆立法委員選舉採用「單一選區兩票制」，國民黨獲票率爲53.5%，獲得78.1%席次，席次偏差甚大。本文關心的是，什麼因素造成這種偏差，與選票空間分布及「選區劃分」有何關係。爲了回答這個問題，作者應用GIS（地理資訊系統）與空間計量方法，探討影響席次偏差的諸多因素，以第六、七屆立委各縣市選票資料進行實證分析。研究發現，席次偏差綠營不能歸咎選區劃分，造成此結果的主因是，兩陣營實力差距拉大，而政黨選區獲票率的標準差過小，因而擴大獲票率與席次比的差距。本文並以GIS圖示方法，個案探討選票集中與席次分配可能的關係。 In the 7th legislative election, Taiwan adopted the single-member district plurality, two-vote system. KMT garnered 53.5% of popular votes but received 78.1% of total seats. What factors account for the bias, and what is the role that spatial distribution of votes and districting plays? To answer these questions, we employ GIS and spatial econometrics to explore the determinants of disproportionality. Our empirical data comprised of the result of the 6th and 7th legislative election. We find that the vote share gap between parties and equally distributed votes across districts are the main contributing factors, while districting does not prove itself significant. On the other hand, we also use GIS to illustrate the relationship between vote concentration and seats allocation in several counties.