GIS deals particularly with existing data from other sources, usually in alphanumeric databases.

But the other techniques will vary depending on the characteristics of the sensor, the property being mapped, the equipment and software at your disposal, the use the map is going to be applied to, and the requirements of the user who will be using it.

Air photo was strictly analog, using mechanical-optical devices, stereo plotters, merging stereoscopic air photo pairs. The primary use was developing contours of terrain for civil engineering and mining support applications. You had to physically see the relief in the terrain and then draw contours, taking into account the ability of vegetation, ground texture, shadows, and other factors in obscuring the 3-d signal.

At 3000' camera above ground you could detect terrain variations as small as 6" under ideal conditions, and contours were typically a foot apart, much of which was a judgement call. This allowed road builders to figure drainage and strip miners to calculate overburden and inventory stockpiles. Map scale at that altitude was typically about 100'/inch or 1:1200.

Satellite imagery was more multispectral related. We worked with Landsat and Thematic Mapper imagery to try and deduce ground geology. Pixel sizes were on the order of tens of meters. This was highly automated, (70s and 80s minicomputer era, HP-3000 and VAX platforms) but our interest was not so much on the location of ground objects, but on their reflective properties across the spectrum, which gave us clues as to their mineralogy.

I also worked a lot with wellog data, information from sensor probes lowered into well holes which gave us various physical properties of the strata the probes penetrated. The data was x,y,z and some measurement taken at that location by the probe. This allowed us to generate 3-d maps of underground rock formations.

I also worked a lot on maintaining software for intelligence and military applications. I can't tell you much about that, but one unclassified project I worked on was the imagery databases used to train pilots how to fly glide bombs and other remotely controlled ordnance.

Late in my career, GIS was mostly used to convert statistical ground truth into thematic maps to guide policy makers in making decisions. For example, given legal requirements as to how close a pervert could live to a school, what areas in the County were available for registered sex offenders to live in. I kid you not. I also worked with 911 emergency dispatch data, maintaing the electronic maps used to send police, fire, and ambulances when somebody called with an emergency. The GPS street data on your car navigation devices came from people like me, constantly updating municipal street and address data bases for 911 purposes.

And of course, I've worked as a map user, too, in maritime navigation, and one of my hobbies is astronomical mapping.

The interesting thing is that even though these applications were very differnt, using different technologies and yielding different products, everything I learned at one job cold be easily transferred to, and was useful, at the next. Prospective employers were delighted at my breadth of knowlege, specific techniques and technology could always be taught on the job. Lately, in order to get a job in mapping today, you have to demonstrate recent competence in a particular type of mapping software, not general cartographic principles. Past experience in related fields doesn't mean squat any more. They just want someone who can work with 'ArcView version 10.0'. Industry doesn't need cartographers, it needs workstation jockeys.

I retired just in time.