change m_map high to intermediate resolution and and high resolution

add simplifications submit by Thierry Reynaud:
  latRange = (latMax-latMin);
  latMin = max(floor(latMin), -90);
  latMax = min(ceil(latMax), 90);

  lonRange = (lonMax-lonMin);
  lonMin = floor(lonMin);
  lonMax = ceil(lonMax);