/usr/include/ is in libspatialindex-dev 1.8.1-2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/spatialindex/
/usr/include/spatialindex/tools/
/usr/include/spatialindex/tools/PointerPool.h
/usr/include/spatialindex/tools/Tools.h
/usr/include/spatialindex/tools/SmartPointer.h
/usr/include/spatialindex/tools/PoolPointer.h
/usr/include/spatialindex/tools/rand48.h
/usr/include/spatialindex/Point.h
/usr/include/spatialindex/MVRTree.h
/usr/include/spatialindex/TimePoint.h
/usr/include/spatialindex/TimeRegion.h
/usr/include/spatialindex/MovingRegion.h
/usr/include/spatialindex/Version.h
/usr/include/spatialindex/capi/
/usr/include/spatialindex/capi/CountVisitor.h
/usr/include/spatialindex/capi/Index.h
/usr/include/spatialindex/capi/DataStream.h
/usr/include/spatialindex/capi/sidx_api.h
/usr/include/spatialindex/capi/BoundsQuery.h
/usr/include/spatialindex/capi/LeafQuery.h
/usr/include/spatialindex/capi/Error.h
/usr/include/spatialindex/capi/CustomStorage.h
/usr/include/spatialindex/capi/Utility.h
/usr/include/spatialindex/capi/sidx_impl.h
/usr/include/spatialindex/capi/ObjVisitor.h
/usr/include/spatialindex/capi/sidx_config.h
/usr/include/spatialindex/capi/IdVisitor.h
/usr/include/spatialindex/LineSegment.h
/usr/include/spatialindex/SpatialIndex.h
/usr/include/spatialindex/RTree.h
/usr/include/spatialindex/TPRTree.h
/usr/include/spatialindex/Region.h
/usr/include/spatialindex/MovingPoint.h