What is the scope of the appellate court's review of the trial court's ruling on the writ of mandate?

Preliminarily we note that on review of the trial court's ruling on a writ of mandate, an appellate court is ordinarily limited to an inquiry respecting whether substantial evidence supports the judgment. However, this limitation is inapplicable to questions of law where the facts are undisputed. In such instances the appellate court is not bound by the trial court's determination but may make its own determination. (Evans v. Unemployment Ins. Appeals Bd. (1985) 39 Cal.3d 398, 407, 216 Cal.Rptr. 782, 703 P.2d 122.) The following undisputed facts were before the trial court.