It seems that the fact that Normandy lies close to the United Kingdom must have played a role. However, parts of the Netherlands and Belgium are (almost) just as close, or even closer. So why not start the invasion there? Where there political reasons (e.g. de Gaulle wanting to have France liberated first) or perhaps military reasons for this choice?
From the wikipedia article of the Normandy landings
"Four sites were considered for the landings: Brittany, the Cotentin Peninsula, Normandy, and Pas de Calais. As Brittany and Cotentin are peninsulas, it would have been possible for the Germans to cut off the Allied advance at a relatively narrow isthmus, so these sites were rejected. As the Pas de Calais is the closest point in continental Europe to Britain, the Germans considered it to be the most likely initial landing zone, so it was the most heavily fortified region. But it offered few opportunities for expansion, as the area is bounded by numerous rivers and canals, whereas landings on a broad front in Normandy would permit simultaneous threats against the port of Cherbourg, coastal ports further west in Brittany, and an overland attack towards Paris and eventually into Germany. Normandy was hence chosen as the landing site."