Map size

The map cell must be small enough to properly sample the synthesized main beam: a minimum of 3 cells per beam is required for CLEAN to work properly. Task UV_STAT can be used to determine the appropriate cell size.

The number of pixel along each dimension must be a power of two for efficient use of most image processing algorithm. Since CLEAN works properly only in the inner quarter of a map, the map size should be twice the region of interest. Remember the primary beam size of the 15-m antennas is 55" at 90 GHz, 22" at 230 GHz.

Map size can be reduced by adequate centering, using the UV_SHIFT variable and associated parameters in UV_MAP or MX, or the UV_SHIFT task before mapping. These parameters can also be used to align the map axis with a feature of interest, by rotation of the UV coordinates. This is especially interesting for bipolar flows or edge on galaxies, for example.