The Institute for the Study of War (ISW) publishes detailed high-fidelity maps of the war in Ukraine, updated daily.
This post provides context on how ISW maps are made, what they mean, and why ISW is a commonly considered a reliable map source.
ISW publishes maps which are updated daily to their interactive map https://isw.pub/InteractiveUkraineWarMap and their Ukraine conflict updates https://www.understandingwar.org/backgrounder/ukraine-conflict-updates. This is very helpful for using it as a resolution source, compared to other maps which update live and don't necessarily have an easily accessible historical archive.
ISW maps are shaded red where they assess that Russia controls the territory based on visual evidence / geolocated footage, and are shaded orange where Russian sources claim control.
As an example, here is a detailed thread by one of the map authors showing how these assessments are done for one day's updates: https://twitter.com/georgewbarros/status/1643403932276858880.
Because map updates are made only after verification based on visual evidence, the red shading is a relatively more conservative and reliable indicator of Russian control compared to the yellow shading and to some other maps, especially in contested areas. It may sometimes tend to lag some days behind other maps, depending on the speed at which visual evidence becomes available. In Bakhmut, advances in the red shading have often been several days behind the yellow shading and other maps. On the other hand, for an example where it updated quickly, after Ukraine retook Kherson, ISW's maps were updated within a day because of the plentiful visual evidence available.
So when an area becomes shaded red on ISW's maps, it means we can be highly confident that Russia has advanced there, whereas on other maps it may represent a lower level of confidence. This has obvious pros and cons (confidence vs latency of updates), just be aware of it when interpreting the maps.
The maps are updated at 3pm ET every day, and the conflict updates are published later that day with the same maps (note that they also say "Assessed Control ... as of 3:00 PM ET")
For reference, other good map sources include: