This example demonstrates an adaptive quadtree-based rendering technique for panning and zooming over geographic data. It visualizes world country boundaries from the visionscarto-world-atlas dataset using a Mercator projection via `d3.geoMercator` and `d3.geoPath`. A grid of points covering the northeastern United States is indexed into a `d3.quadtree`, which is then traversed during zoom to draw colored rectangles that subdivide the viewport only to the necessary depth, with a visible cutoff threshold. Pan and zoom interactions are handled by `d3.zoom` and `d3.zoomIdentity`.