We show NOTAM on the map when they are establishing airspace, or some sort of activity contained in a geographical area (or route) that you may well wish to avoid or at least know about.

There are a great many more NOTAMs that are not depicted on the map because graphical depiction simply doesn't make sense, for example something about the situation in Syria, or a navigation aid being out of service, or an administrative change to an airfield.

Thank you, I follow your logic. The odd thing is that we close the airfield for events quite often and I'm almost certain that this was previously indicated by a circle on the chart. Perhaps I recall incorrectly. The other odd thing is that this Notam is not visible at all as far as I can see via the NotamInfo site (although the nearly identical historical ones are). That is clearly nothing to to with you but was just another indication to me that something odd was going on.

The airfield is Notam'd closed this weekend (15th to 18th). I have set my flight details to the active period but there is no indication of the Notam on the planning chart. The Notam text appears in the Notam list and clicking "Show on map" does highight the correct area, but it is otherwise invisible. Am I being dim?