Well, where I work, we use orthographic imaging. Basically, a plane with a camera or series of cameras fly over an area in a very specific and preplanned flight path and at differing altitudes. Pictures are taken in parallel lines (either up and down as in following latitude or side to side, following longitude).
These images are later stitched together. They are high resolution photos, so based on the optical/focal settings used on the camera lens and the altitude(s) used to take pictures, they can calculate a scale (zooming) in which each corresponding altitude that a map represents to the resolution of the orthograph (basically an aerial image).
Remote sensing includes aerial photography. It also includes the use of satellite imagery (either optical or radar), shipping (radar and sonar), even weather buoy network. All of these methods can be used to produce some type of map showing what ever features you want. This could include buildings, elevations, water, surface, or air temperatures. From all of these sensors, you can literally develop a useable map from these alone, depending on your needs/requirements.
