Website performance: loading markers on Google Map from a Google Fusion Table v/s locally stored JSON file

Question

Why does website performance improve very significantly when (for example, 100,000) markers are loaded on Google Maps from a Google Fusion Table versus loading the markers from a locally stored JSON file storing the same data

Answer 1

FusionTablesLayer uses tile based rendering (the tiles are rendered on Google's server), loading a DataLayer from a JSON file doesn't, your browser loads the file locally, then renders the data.