Basic Index Mapping / Pre-Basic Index Mapping. BIM and Pre-BIM describe parcel mapping of lower spatial accuracy than POLARIS. BIM quality parcel mapping was derived from moderate quality base mapping, at scales of 1:10,000 or less for areas of Ontario where legal surveys or control points are not consistently available. Pre-BIM is the lowest quality mapping for areas where base mapping is not available. The locational accuracy of BIM and Pre-BIM mapping in highly variable and comes with no guarantees of quality.