OpenCities Map preserves circular 2D arcs, but strokes 3D arcs. This means that 3D arcs will be posted and queried as linestrings rather than the original element type. Ellipsoid (or non-circular arcs) and b-splines are only supported as 2D in SS4 and CONNECT.
To ensure that the queried linestring approximates the original arc as close as possible, set the ECSDK_GEOMETRY_STROKING_TOLERANCE to a value like 0.001 or 0.0001. The value represents the maximum distance between the original arc element and the sroked linestring in master units. The smaller the value, the closer the approximation to the original arc.