NASIS Map Unit ID & Legend Map Unit ID history related to SSURGO MUKEY

With NASIS 6.0, the source of the content of the mukey column in SDM data changed from the muiid in the Mapunit table in NASIS to the lmapunitiid column in the Legend Mapunit table. During the 6.0 conversion lmapunitiid was set to = muiid since at that time there was a one-to-one relationship between records in the Mapunit table and those in the Legend Mapunit table. This allowed us to get by without having to recertify all existing spatial data and inserting new mukey values. At that time we also generated the National Mapunit Symbol which is the Base31 version of muiid in the Mapunit table. So now, each record in the Mapunit table actually 2 nationally unique identifiers – National musym, and muiid in NASIS.

Now the fun starts. Since the release of 6.0 users have been doing just what you describe below, and it is what is intended to happen during MLRA recorrelations and updates through time. For example, prior to 6.0 you had something like the following:

Immediately after the 6.0 conversion you had something like the following:

Now you have looked at these 3 map units and maybe have decided that they really are the same beast. So, you decide to correlate them together and choose “alpha silt loam, 1 to 4 % slopes” as the new correlated name. the resulting table would look something like the following:

Nothing is messed up in SSURGO. The mukeys remain the same and still link to the spatial features. One set of data (DMU) is being presented for all 3 local musyms (Aa, 123, and AC) and they all carry the same map unit name and national mapunit symbol.