Location, location, location. It's the most important thing in real estate, and since an arco is a big real estate development project, it would be important here, too.

There are two basic ideas...to build a space completely independent, away from other urban areas. It would be the most pure form of the independent living idea of an arco, a lone tower rising alone in the natural surroundings, but probably not practical for getting people to move in. However, to build it in an urban area, such as a major city like New York, it would likely be treated as just another large building. Why would the government services required for a true arco be moved into the building if they're just a subway ride away? Would it really be green if people were constantly walking out the front door and hailing taxicabs to take them to places outside the arco?

And would such a sizeable structure be built if it blocked the sun and views from a substantial number of smaller surrounding buildings?

No, an arco would almost have to be built away from other structures, but it can't be truly isolated. An ideal location would be at the convergence of road and rail transportation and hopefully plentiful fresh water supplies, near enough to a large city to connect to its local rail transportation and far enough away to make it independent of that city.

It should also be considered what types of natural catastrophies should be expected in a particular location. For example, I don't think San Francisco would be a great spot to put down the world's largest structure. The desert outside Las Vegas would work for protection from natural disaster, but a drought would likely be catastrophic to the community because of how many thousands of new people that would be added to the already strained LV water system. Texas has tornadoes, Miami has hurricanes...