[Vrul]

This may look a bit like overkill but here is what I'm using (the coordinate stuff is a modification of code provided by elcius):

local GetBestMapForUnit, UnitPosition = C_Map.GetBestMapForUnit, UnitPosition
local GetWorldPosFromMapPos = C_Map.GetWorldPosFromMapPos

local mapID, offsetX, offsetY, scaleX, scaleY, vector = nil, { }, { }, { }, { }, CreateVector2D(0, 0)

local mt = { __index = function(self, mapID)
    vector.x, vector.y = 0, 0
    local _, offset = GetWorldPosFromMapPos(mapID, vector)
    vector.x, vector.y = 1, 1
    local _, scale = GetWorldPosFromMapPos(mapID, vector)
    offsetX[mapID], offsetY[mapID] = offset.x, offset.y
    scaleX[mapID], scaleY[mapID] = scale.x - offset.x, scale.y - offset.y
    return self[mapID]
end }

setmetatable(offsetX, mt)
setmetatable(offsetY, mt)
setmetatable(scaleX, mt)
setmetatable(scaleY, mt)

local frame = CreateFrame("Frame", nil, UIParent)

local timer, X, Y = 1
frame:SetScript("OnUpdate", function(self, elapsed)
    timer = timer + elapsed
    if timer < 0.1 then return end
    timer = 0
    local x, y = UnitPosition("player")
    if x and y then -- Reversed axis
        x, y = (y - offsetY[mapID]) / scaleY[mapID], (x - offsetX[mapID]) / scaleX[mapID]
        if x ~= X or y ~= Y then
            -- Update coordinates stuff here
            X, Y = x, y
        end
    end
end)

frame:SetScript("OnEvent", function(self, event)
    mapID = GetBestMapForUnit("player")
    if mapID and UnitPosition("player") then
        self:Show()
    else
        self:Hide()
        timer, X, Y = 1, nil, nil
    end
end)
frame:RegisterEvent("PLAYER_ENTERING_WORLD")
frame:RegisterEvent("NEW_WMO_CHUNK")
frame:RegisterEvent("ZONE_CHANGED")
frame:RegisterEvent("ZONE_CHANGED_NEW_AREA")