[Baertram]

Is there a parent of the world map containers? e.g. is ZO_WorldMapContainer the parent of ZO_WorldMapContainer1?

Then do:

local numChildren = <parentOfWorldmapContainers>:GetNumChildren()
for i=1, numChildren, 1 do
 local childOfParent = <parentOfWorldmapContainers>:GetChild(i)
 childOfParent:setSomething(thing)
end

Else do it like this:

local numWorldMapContainers = 81 --maybe there is a better way to ge the 81 dynamically from the active map's ID or similar?
local templateName = "ZO_WorldMapContainer"
local WM = WINDOW_MANAGER
for i=1, numWorldMapContainers , 1 do
 local worldMapContainer = WM:GetControlByName(templateName , i) --Will create a control with name "ZO_WorldMapContainer1" and so on
 worldMapContainer :setSomething(thing)
end

If you describe here (https://gitter.im/esoui/esoui) what you want to achieve I bet there will be even an easier/better way that devs like votan (who got a good knowledge of the worldmaps) can hep you with.