master maps: Mapping grid-based statistics using OpenLayers, Three.js and D3.js + https://blog.mastermaps.com/2015/11/mapping-grid-based-statistics-with.html D3.js v4/v5 ヒートマップ(heat map)の作り方 – データビジュアライゼーション・ラボ + https://wizardace.com/d3-heatmap/ Program 1 Description + https://people.ucsc.edu/~ydchoe/CMPS%20161/prog1/prog1.html