A number between 1 and 6 that represents the range of scales that include the actual compilation scale of an ENC. The range of scales associated with each scale band is similar for each nation, but not identical. See Tables 1.5-1 and 1.5-2 in our textbook Introduction to Electronic Chart Navigation: With an Annotated ECDIS Chart No. 1. The scale band of an ENC is always part of its chart number. The ENC named US5WA16M is scale band 5 meaning its actual scale must be between 1:5,000 and 1:50,000. The actual scale of this chart is 1:40,000.
A twist to this concept for the moment is this: NOAA is in the process of "rescheming" all ENC, and this process changes the definition of US scale bands to match the international values. The summary is shown below.
Scale bands are often referred to as "Usage Bands," implying this is the same concept, which is not true, but not often a problem. There is logic in separating them, where the scale bands are the numeric indexes to the scale ranges that also go directly into ENC chart names, and usage bands are the typical applications. The distinction comes up with the use of paper charts that have defined usage bands that are different from those associated with ENC. As we transition to the new form of paper charts (NCC) while at the same time progressing with the rescheming program, the definitions shown above should become the standards. Needless to say, some references will remain outdated for a period of time. The transition to all paper charts being NCC will be complete by December, 2024.