How much consideration did the Allied planners give to say invading closer to Germany for example Denmark?
Also how much though did the Allied Planners give when choosing a location, to the type of countryside in the Normandy area?
The two main contenders for Western military planners were the Normandy coast, and Pas-de-Calais.
The early variations of a cross-channel invasion plan in 1942 and 1943 gave careful consideration to a landing in Calais. With only 12-13 miles across the Channel from Dover, it was the shortest route over the sea, and provided an advantage of being a shorter trip to Berlin. Additionally Calais would have in theory been well designed to handle the logistical issues of troop deployment, and acting as a highly capable supply throughput. The greatest obstacle it contained was that Germany recognized all of these factors as well, and it was armed/fortified to the teeth. It was thought to be the obvious choice for a main invasion spearhead.
Regarding landing sites outside of Normandy, their greatest purpose in the end were for strategic deception. Allied planners did everything in their power to deceive the German High Command (OKW/OKH) that they would possibly invade a number of areas. Operation FORTITUDE (North and South) and Operation BODYGUARD took elaborate measures to create the appearance that major invasions of Norway (via forces stationed in Eastern Scotland) and Calais (via FUSAG in East Anglia) were the main invasion thrusts. Furthermore reinforcing the notion that Normandy was a diversionary attack, hence causing Hitler to redeploy considerable forces to Norway, and Calais.
Neither of these forces ever existed, and in the case of Calais, it kept considerable forces there for two months following the Normandy landings awaiting an invasion that would never come. Eisenhower believed he needed 48 hours without a significant German counter-attack after establishing a beachhead in Normandy to succeed.
What is often forgotten is Operation DRAGOON: the amphibious invasion of southern France. Originally it was planned to commence simultaneously with OVERLORD, but was delayed due to a lack of landing craft because of operations in other portions of the Mediterranean Theatre. It did not proceed until August of 1944. Had it proceeded as originally planned, it likely would have had a far more decisive impact on the invasion of France. By the time DRAGOON moved forward, German forces in southern France had largely withdrawn.