[DahkCeles]

If you are trying to build an overlay over the entire map frame (its borders, UI elements, etc.), then something like this might help:

local function myFunction()
  local isMaximized = WorldMapFrame:IsMaximized()
  -- do something
end
 
hooksecurefunc(WorldMapFrame.BorderFrame.MaximizeMinimizeFrame, "Maximize", myFunction)
hooksecurefunc(WorldMapFrame.BorderFrame.MaximizeMinimizeFrame, "Minimize", myFunction)

If you are trying to build something on the map canvas itself which appears at an x/y coordinate and can be dragged to another x/y coordinate, then you should take a look at MapCanvas_DataProviderBase.lua.

MyAddonSavedVariables = { }
 
MyPinMixin = CreateFromMixins(MapCanvasPinMixin)
 
MyPinMixin:OnAcquired(id, x, y)
    self:SetPosition(x,y)
    self.id = id
end
 
MyPinMixin:OnLoad()
    -- placeholder appearance for testing
    self:SetSize(20, 20)
    self.texture = self:CreateTexture(nil, "ARTWORK")
    self.texture:SetTexture("Interface\\RaidFrame\\UI-RaidFrame-Threat")
    self.texture:SetAllPoints()
 
    -- draggable to a new map coordinate
    self:RegisterForDrag("RightButton")
    self:HookScript("OnDragEnd", function()
        local x, y = self:GetMap():GetNormalizedCursorPosition()
        x = x and Clamp(x, 0.05, 0.95) or 0.5  -- stay a little inside the box
        y = y and Clamp(y, 0.05, 0.95) or 0.5
        MyAddonSavedVariables[self.id]["x"] = x
        MyAddonSavedVariables[self.id]["y"] = y
        self:SetPosition(x,y)
    end)
end
 
MyDataProvider = CreateFromMixins(MapCanvasDataProviderMixin)
 
MyDataProvider:RefreshAllData()
    self:RemoveAllData()
    for id, coords in ipairs(MyAddonSavedVariables) do
        self:GetMap():AcquirePin("MyPinTemplate", id, coords.x, coords.y)
    end
end
 
WorldMapFrame:AddDataProvider(MyDataProvider)
 
 
-- placeholder just to create a single pin for testing
local listener = CreateFrame("Frame")
listener:RegisterEvent("PLAYER_LOGIN")
listener:SetScript("OnEvent", function()
    if #MyAddonSavedVariables == 0 then
        tinsert(MyAddonSavedVariables, {0.5, 0.5})
    end
end)

<Ui>
    <Frame name="MyPinTemplate" mixin="MyPinMixin" virtual="true"></Frame>
</Ui>

## SavedVariables: MyAddonSavedVariables

Disclaimer: I just quickly wrote this together by taking snippets of a much longer file. I'm probably missing something to make it work.