Maps vs. Air Photos
Now that everyone with an internet connection has access to Google Earth and Google Maps, we all have access to some fairly high quality air photo imagery. This might seem to be a good thing, but there are problems with air photos. They are not maps.
A map is a representation, or an interpretation of reality (most often derived from air photos), with information added to it from land survey data, elevation data, etc. For example, while an air photo can show you what the ground cover is, and where the roads are, the map shows you the contours (indicating elevation), road names, the scale, what what the land use it (industrial, residential, park etc). While some may argue that Google Earth “Satellite” view is a map because it overlays the roads and such, it still suffers from too much information, and not enough of the correct kind of detail that can be offered by a well designed map.
A topical example is provided below. The recent explosion and sinking of the Deepwater Horizon oil rig in the Gulf Coast.
The Satellite image shows the oil slick in relation to the coastline.
The status map, on the other hand, shows scale and geographic grid. It shows the extent of surface oil and the quality of the slick as observed by survey flights. It shows specific distances from points on the slick’s front to points on the coast for reference. It shows the exact position of the incident, including a reference latitude and longitude, it shows staging areas, it includes the date and time of the data, etc.
It’s not that the map provides more data, it’s that it provides more useful data, provided and interpreted by experts, and data that is not available on the air photo. It provides context and it tells a story. It’s easier to read and get a sense of what is going on.
All of this may seem to be obvious, but I still come across people who do not understand that a map as an interpretation of reality is in most cases more useful than an air photo.
I think that your interpretation of "more useful data" is perhaps a bit bias. I think it depends on exactly what data you are looking for. First a map has to actually include the details that you are looking for. Your USCG map shows good information regarding the oil slick. However the map was probably built by "the experts" interpreting air photo data (and other information). The the air photo will also be referred to in the future by these experts as it is a exact historical record of the condition of the slick at the exact time that the photo was take.
Ortho photos provide different information than maps and allow the user to pick out whatever information they want, rather than the info that the map maker decided should be included. A road map doesn't provide any information regarding the vegetation cover for example. (I admit that the ortho photo doesn't give you the road name) I've seen ortho photos used for timber typing, municipal development and even to assess the probability of old buried fuel tanks.
From a SAR perspective, an air photo might allow you to locate a potential heli landing spot. A map could only provide this if that info was specifically documented.
Finally, I have never found a map that could provide me with a 3D view. I have used consecutive 3D ortho photos to accurately measure the height of an object.
I'm not sure if I was clear enough in the post, but I think we essentially agree.
It's the interpretation here that is the issue. An expert can interpret an air photo and create a map from it. The map embodies the expert's knowledge and although it contains less overall information, it contains relevant information (in the context of the map's theme), and in an easier to read format.
For navigation I do not need a picture of each individual tree, but I do need to know the elevations. Thus I get contours. I also want to know where the clearings and roads are, so I get a roadway layer and a land cover layer.
At times the air photo can be used as you say for a detailed analysis of a specific local area for tree type and height, and it's always good to have them available to refer to when necessary. But for most purposes, including navigation, a map designed for the purpose is far superior.
You’re bang on: a picture is not a map. End of story!
Thanks for the comment on an old post!