Any performance difficulties related to List?
As was said in the comments, I don't think List&lt;T&gt; makes any significant difference over an array.

But with a bit of LINQ you can reduce the nesting a bit:

foreach (var b in map.bases)
{
    foreach (var c in map.points.SelectMany(cc =&gt; cc))
    {
        CalculatePointValues(c, b, los);
    }
}


And it could be worth trying to profile it with some Parallel looping as well:

Parallel.ForEach(map.bases, b =&gt;
    {
        foreach (var c in map.points.SelectMany(cc =&gt; cc))
        {
            CalculatePointValues(c, b, los);
        }
    });