For starters, if anybody is still using Thomas Brothers, they are using outdated map books. They no longer publish current and traditional hard copies. In landlocked areas with little change - this is no big deal. But for areas like Sac County, they're worthless.
Fire does not use Thomas Brothers - they use a highly customized and very "large" and comprehensive mapping system. MANY hard copy binders are need for each area/district. Fire department needs are much different than law and the maps must be easier to read - fire hydrant, gas, electrical access etc
The last fire map book I saw was for Citrus Heights and it was huge. Each page only covered a couple streets. Today, I'm sure a lot of the "field" map books are digital. That's just a guess though.
Today a lot of mapping systems are purely digital - Their foundation is ESRI and entities such as
SACOG and
Pages - Welcome to Sacramento County GIS help with coordination and dissemination of data. A lot of this is public information.
Obviously digital maps are highly customized - but they are also very easy to share and easy to keep updated. Some mapping systems even utilize API from third party entities - Traffic / Weather / GPS