why did the allies choose omaha as one of the landing beaches at normandy?

Landings at Omaha were necessary to provide a link with the British and Canadians to the east and the US landing at Utah beach,thus providing a continuous Allied front from D-Day onwards.The Utah beach landings were planned as the area from which US troops could move swiftly to capture Cherbourg,a large port with a deep water harbour which the Allies wanted to land supplies quicker.(Cherbourg was not captured quickly, the port and dock facilities being largely destroyed by the Germans before the Americans could capture the whole city).

The whole of the French coast opposite England was heavily fortified,and the casualties at Omaha were partly a result of the failure of the first waves of assault troops to land in the correct place;the current took their landing craft some distance from the intended landing point,and these landing craft ran aground on sandbars some distance from beaches.As a result the troops they carried had to wade several hundred yards to shore,exposed to enemy fire.Many of the tanks that attempted to support the infantry also had difficulties making the extra distance from the sandbars to the beaches,most of them sinking.

Omaha beach was only a part of the overall invasion. The Allies had to attack on a sufficiently wide front to prevent the Nazis from concentrating all their forces at the point of attack. Also, the amount of men and material being landed would operate more efficiently in a wider area. The broader front gave landing craft more room to maneuver and gave the men on the beaches some room to spread out. The Normandy area was a logical area for the invasion, because it was a gateway to an area that could be established as the Allies' foothold on Europe.

As CMV tried to explain the landing craft at Omaha Beach put the 1st Infantry ashore a mile away from where they were suppose to. No commander purposely puts his troops ashore at the foot of heavily defended cliffs with a very few places to exit the beach and then only by blowing obstacles out of the way. When BG Roosevelt (He was the senior officer on the beach at the time) realized that they were in the wrong place he made the decision to start from there rather than evacuate the beach and come back where they were suppose to land.

You've already got good answers here, but I just wanted to add that most of the men on Omaha beach got dropped at the wrong place. In fact, most of what happened on D-Day was a whole series of errors, from the airborne misdrops to the Rangers at Pont du Hoc, who lost most of their men taking a gun position that wasn't even there. Utah Beach, which was much lower in casualties, was way off where they were supposed to land. If they had landed in the right place they would have been slaughtered, too. The operation was so big and so well planned that there was room for good luck and bad luck.

Due to the fact that that was the place the Germans least expected them to land. The entire German 15th military was once ready for them at Calais which is where they have been expected. Apart from the only real massacre used to be on Omaha seashore and that was once seeing that the touchdown craft put the 1st Infantry Division ashore a mile faraway from the place they have been suppose to. They weren't think to come ashore beneath these cliffs in any respect.

Landing craft fitted with ranks of thousands of artillery rockets were supposed to carpet the beaches with explosions to detonate any mines there , and to provide shallow sand craters for shelter , but the lead navigator of that flotilla got his position wrong so they all fired to soon and hit the sea instead .

Cant blame the guy , smoke and spray everywhere and a featureless coast .

Also the strong wind not only pushed the landing craft for troops into the wrong locations , it dispersed the smoke screens being dropped and fired .

Also Air control was being done from fighter direction ships far out in deep water , because using air support as flying artillery was not yet fully worked out , so there were few controllers up with the troops to mark ( coloured smoke ) and call down strike aircraft .

Also aircraft were being kept out of the low-level altitudes to allow for free naval gun support - cant do both in the same airspace .

Also the heavy casualties meant that communications broke down and the waiting ships could not fire in support - cant blame them , the haze of smoke and airborne moisture meant they couldn't see .

They knew that they would have to land against a heavily entrenched force anywhere they would land. And it was part of their strategy to invade over a large area. Of the five (contiguous) "beachheads", Omaha was the most heavily defended (and thus was given to the Americans to take); but it was hoped that the massive pre-invasion bombings of the area, linked with the elan and training of the troops and their naval support, would allow them to be victorious.