Projectionmmapped

Projectionmmapped is a specialized data access technique that combines spatial projection data management with memory‑mapped file systems. The method uses operating system support for memory mapping to load projection parameters—such as coordinate system definitions, transformation coefficients, and datum shift values—directly into a process’s address space. This allows applications to access projection information through pointer arithmetic rather than performing file I/O or database lookups, resulting in lower latency and reduced CPU usage.

In practice, a projectionmmapped implementation stores projection metadata on disk in a contiguous binary structure. When an application requires the data, the file is mapped with read (and occasionally write) permissions, and the projection library references the fields in place. This approach is well suited to geographic information system (GIS) software, cartographic rendering engines, and spatial databases that must handle large numbers of coordinate transformations at high speed. Because the operating system manages paging, only the portions of the projection table that are accessed are loaded into memory, keeping overall memory consumption efficient.

The technique emerged in the early 2000s with the rise of high‑resolution global datasets and increasingly complex datum shift files such as the NADCON and NTv2 tables. Many modern GIS libraries—including parts of the PROJ project and open‑source spatial databases like PostGIS—offer optional projectionmmapped support. While the concept improves performance, it also introduces dependencies on OS‑level file system stability and requires careful cache‑coherence management when projection tables are updated.