Tags are labels you invent and apply to units. They are the most flexible organising tool on the Plan tab, because you can have as many as you like and a unit can carry several at once.
Anything you might later want to filter back to is worth a tag — a client's preferred sites, a phase of the campaign, units pending a decision.
Tagging In Bulk
This is the fastest way, and the one to learn:
Filter to the units you want, if a filter helps.
Draw a shape around them on the map.
In the Tags section of the panel, apply your tag.
The panel shows the tags already present on units inside your shape, so you can see what is there before adding more.
Clear Tags in the same section strips tags from everything in bounds.
Tagging By Market
To label every unit with the market it sits in, use Add Market Tags to Units from the Tools menu. It tags the whole campaign in one action, rather than you drawing around each city.
This is worth doing early on a multi-market campaign. It makes the Tags filter into a fast market switcher for the rest of your work.
Filtering By Tag
Tags appear in the Tags filter in the filter bar. Selecting one narrows the map and the unit sidebar to units carrying it.
This is what makes tagging worth the effort — a shape you drew once becomes a set you can return to in two clicks, without redrawing it.
Choosing Tag Names
Tags are free text, which means they are only as useful as your naming. A few habits that hold up:
Be consistent. "Phase 1" and "phase one" are two different tags and will split your set.
Prefix related tags. "Client: approved" and "Client: rejected" sort together in the filter.
Tag the decision, not the obvious. Media type and vendor already have their own filters, so tagging those adds nothing.
*Note: Tags are shared with everyone on your account who can see the campaign, unlike favorites which are personal. Name them so a colleague picking up the campaign can tell what they mean.