This paper presents the development of a Web API that enables querying PLATEAU 3D city model attributes using Japan's Spatial ID referencing system. We implemented a three-tiered API architecture that provides flexible access to city model data for 250+ Japanese cities with median response times of 35ms. An interactive interface allows users to visually select and explore Spatial IDs. Our implementation revealed that the current Spatial ID specification's geoid-based vertical reference creates integration challenges with common 3D visualization platforms and positioning systems. We propose improvements including adopting ellipsoidal referencing or a more fundamental geocentric approach. This work advances Japan's digital-twin ecosystem by providing a standardized mechanism for integrating diverse urban datasets through universal spatial referencing.