A resolution of 2 to 3 feet means that features as small as 2 to 3 feet across can be distinguished, regardless of sensor technology. This is different from saying "2 to 3 feet per pixel" because the resolution of the lens and atmosphere may be worse than the resolution of the image sensor or film.
Consider a <$100 consumer digital camera with a hypothetical 12MP sensor (4000x3000 resolution). Suppose you point the camera at a 40' by 30' wall with a highly detailed pattern. Though the actual sensor resolution to wall resolution would be 0.01' per pixel, due to various optical distortions (and possibly the Bayer filter on the sensor), the effective resolution could be closer to 0.05'. Thus, any element of the pattern printed on the wall that was smaller than 0.05' would be unresolvable.
Consider a <$100 consumer digital camera with a hypothetical 12MP sensor (4000x3000 resolution). Suppose you point the camera at a 40' by 30' wall with a highly detailed pattern. Though the actual sensor resolution to wall resolution would be 0.01' per pixel, due to various optical distortions (and possibly the Bayer filter on the sensor), the effective resolution could be closer to 0.05'. Thus, any element of the pattern printed on the wall that was smaller than 0.05' would be unresolvable.