I spend an unacceptable amount of time 'flying' around the country (U.S.) via Google Earth and I'm always zooming in on airplane symbols to have a look at airfields. In the western U.S. there are lots of rural strips that have the little aircraft symbol on them which I'm presuming come from the FAA. Some of these fields appear marginal at best as legitimate airfields, especially the ones that are obviously part of a farm or ranch.
My question is what level of improvement is necessary for a field to be listed by the FAA as an airstrip? Is there some minimum length, width, slope, etc.? Is there some inspection that is done before you can get put on the charts and are there any ongoing checks to make sure the field is still there when the charts are updated? Does the owner of a strip assume some ongoing obligation as a result of their strip showing up on a sectional?