A somewhat off-topic excursion into the backgrounds of texturing schemes:
I'm not aware if anyone has been doing work to improve the look of the surroundings of FlightGears default airport KSFO, but if I had one area to name it would be San Fransisco Bay.
I've been to the bay area once in real life, and from my memory, the default texturing scheme gave a decent account here. There are no major clashes I'm aware of, and that's much more than can be said for other areas of the world. It's a good idea to regionalize that since it's sort of a showcase for FG, but admittedly I don't find it interesting enough to do it myself.
As for well-matchedness of the dds textures, they seem to be optimized for European use. Look at Hawaii (since I have most of the comparison ready):
West Maui for real:
West Maui in default texture scheme:
Well, we do get the overall color balance wrong, but what gets often overlooked is that this is a texture scheme which really does the whole world - so it will never be spectacular anywhere. What is not appreciated is that it also doesn't get major clashes, unrealistic contrasts, ...
West Maui in dds texture scheme:
Now we're getting more than just the color balance wrong - we're getting harsh contrasts between the rather bright fields and the deep green shrubland and the European-style agriculture really looks wrong here.
The dds basically makes a bet - it has many textures with deeper and more intense colors and commits to a particular style of agriculture - where that bet works out, dds looks more spectacular, but where that bet doesn't work out, the dds set fails really spectacular.
(I'm not posting the regionalized comparison here because that would be an unfair comparison).
Auyantepui (South America) is a really spectacular failure
For real:
And in dds:
My point not being that the dds set is worse. But it's not unconditionally better matched, in many areas of the world the unambitious, low contrast, a bit dull default texture scheme does a mediocre job but hides flaws in the landcover data whereas the high-contrast, more spectacular dds set highlights the same flaws and draws attention to them. I think you may be underestimating the virtue of a texture set which sort of works almost everywhere, even if it's never really right.
As for resolution, the default textures are I think usually 512x512 spread to 2000 x 2000 m, which gives a pixel size of 4x4 m. I'm not sure how large the dds base size is - probably similar. They're mapped to a variety of sizes, but 1000 x 1000 m seems the usual. Which gives a pixel size of 2 x 2 m. The pricetag is that cropgrass1.png is 617K , cropgrass.dds is 2.7 M, so the dds textures take ~4.5 times the diskspace (and download bandwidth) of their png counterparts (imagine how a widespread switch to dds would blow up the size of the GIT repository...)
Edit: It turns out I am wrong in the estimates here - the dds set has 2048x2048 resolution as Emilian points out, and at this size per storage space is quite a bit more efficient than png. The pixel would also then map to something like 50cm x 50 cm.
The better pixel size comes at increased tiling artefacts, which the dds set counters by having very low contrast
inside the texture so as to create no visual cues to tiling. However, contrast inside the texture is an important device to hide the hard landclass boundaries (see the long version of this argument
here, so from higher altitude, the dds set to first oder looks like the mapserver image of the landclass distribution painted with almost monochromatic colors. If you fly low dds is better, but if you're high up dds becomes more dull
Here's an older comparison:
dds (note the absence of any structures in the forest areas - looks almost like monochromatic green):
non-dds (note how the forests show structure because the texture has structure):
Again, my point not being that the dds scheme is bad, but being that there's a lot of things to consider and that many advantages of dds come with a pricetag and translate into disadvantages elsewhere.
Bottomline being - I have been thinking really a lot about texturing and how to make it better, what works, what fails, and what advantages and disadvantages of every scheme are. I might be biased to some degree since my work is on the repo as well, but I am fairly sure if I were convinced that the dds scheme is superior, I would do dds textures... Especially for Europe custom scenery (where the landclass boundaries are nice and the agriculture texturing fits) and from low altitude, dds tends to give the better results in most cases. In default scenery away from Europe from moderate to high altitude, the situation is reversed.
Final note: The discussion becomes a bit moot when you compare both schemes to what procedural texturing can do - because suddenly you can get 10 x 10 cm per pixel in closeup-scenes of the terrain
and at the same time get rid of tiling artefacts at almost any size scale. So my answer to the texturing problem is the procedural scheme, because that can generate you spectacular visuals for any distance.