The length operator for tables does not account for string-indexed entries in itself. You can just use an array instead, like so:
local MAPS = {
{Grassland = serverStorage:WaitForChild("Maps"):WaitForChild("Grassland")}
}
Or just make your own function to count the number of entries in the table, including string-indexed entries by iterating over all of the elements with pairs:
local function count(tbl)
local total = 0
for index, value in pairs(tbl) do
total = total + 1
end
end