I struggle telling apart asphalt and concrete

[marie-bnl]

I read on the Internet that concrete is very rigid and light gray while asphalt is way darker and more flexible, however the roads in my city are all tagged surface=asphalt although they are as light as concrete and feel very rigid.

I think brand new asphalt would be rather easy to tell apart, but old asphalt / concrete look indistinguishable to me.

The pictures in the app aren't very useful either because it's hard to see what is relevant, the color is not helpful, the surface looks the same, there are some cracks and seams but I'm not sure these can be relied upon.

Maybe this is a quest I should leave to car drivers? I'm a pedestrian, maybe drivers do feel the difference.

[matkoniecz]

Can you share a photo? This may enable others to help.

(also, you can disable quest in settings if you want)

[marie-bnl]

I am not trying to answer this for a particular road, I'd like general advice on telling them apart and I think plenty of users can find examples of old asphalt, but I can share a photo tomorrow if that helps.

I also have disabled the quest but I am probably not the only person struggling with that so I'd like this discussion to serve as a source of information for others who do.

Moreover I'd like to think about edits that could be made to StreetComplete, for example editing the pictures, adding textual tips... I feel like no quest should assume you're a road engineer.

[ERYpTION]

Instead of disabling the quest have you considered simply answering 'Paved (generic)' when in doubt? I would think this is still of value for routing engines.

[marie-bnl]

Doing this is misleading, it would suggest: "I did the survey and the road is paved but in a material that is not in the list".

The quest would then not appear to other user since the road surface now has value. Additonally the source of my edits is a survey and you should probably trust survey more than any other source. So fixing the road surface would require a user to be interested in this particular road, survey it, edit it in an external editor and not trust that I selected paved because it was the most appropriate choice. It is equivalent to condemning the road surface to be overly generic for virtually ever.

IMO it is better to leave the road surface undefined until a user gets the quest and is able to answer precisely.

[ERYpTION]

You could be right, although it seems highways tagged 'Paved (Generic)' have their own distinctive color (black) in the SC surface layer, which at least for a SC mapper it should make it easy to notice that these could still use a more accurate surface description.

I would be curious to see those road surfaces, that are so difficult to distinguish. I wonder if they are a special kind not used where I live. It is very rare that I have had any difficulty distinguishing asphalt from concrete, in aerial photographs sure, but not up close.

[mnalis]

The "concrete" picture in StreetComplete should show a line between two pieces (if it is visible on your phone; it is rather thin at those small sizes). Concrete is in majority of cases¹ made of (usually equally sized) blocks (either cast in place, or pre-cast and then brought on location) so you can spot them by regular gaps between those blocks every few meters. See gallery here for few examples.

Asphalt, on the other hand, would easily be continuous for kilometers at a time (unless there were damages and repairs done on it, but it should be looking quite differently and sporadic/asymmetric).

Also, if the road has those "patches" repairs (see this gallery under "asphalt" row, especially "intermediate" and "bad" columns), that is good indication it is an asphalt. Concrete cracks looks differently (also visible in that gallery) and when it cracks, it won't be repaired/patched but will remain broken in majority of the cases.

I'm a pedestrian, maybe drivers do feel the difference.

Yes, even cars, but especially cyclists or roller blades will feel those gaps (there is also some difference in traction where rubber tires will usually have better contact with asphalt then with concrete especially in summer, but that is much harder to tell).

Maybe this is a quest I should leave to car drivers?

If you are still unsure, yes. I would generally suggest that people always disable StreetComplete Quests that are confusing, hard to solve, or otherwise mentally taxing or feel more like work more then like fun. There are always other mappers who will pick them up².

Footnotes

1. although there are cases where concrete can be cast in one piece (e.g. if it is short enough - for example some small pedestrian bridges of few meters over small streams might be cast out of single piece of concrete), those are quite rare in my experience. ↩

2. and if the app does not feel fun in addition to being useful, most people will eventually stop using it completely (which is much worse outcome then if they disabled half the quest and continue solving only those that didn't bother them). ↩