The goal of the Loss of the Night app is to track how skyglow is changing worldwide. But since it was only released in 2013, it will be a while before we'll really be able to see the changes. But the Globe at Night program is already in its tenth year, so the time series is already relatively well developed.
The best place to make a skyglow observation is someplace very close to your home, so that you can observe there again in the future. But if you are willing to travel a kilometer or two in order to help us track how is changing, you could help us out by making an observation near the same place one was made in the past.
The map above shows 5,000 locations on Earth where someone made an observation in the past but there hasn't been a new observation within the last five years. If you can make an observation near to one of these points (or if you have a friend who lives close to one of them), it would be extremely helpful.
You don't need to go to the exact point shown (in fact, I shifted the points by some distance to preserve anonymity). An observation within about 100 meters is close enough.
Update January 6, 2015: During last year's Globe at Night campaign, 24 of these locations were re-sampled. Big thanks to those who took part! The relatively small number means that the revised map for 2016 looks very similar to this map, so I will just leave this one up for now and will probably revisit this idea next year. In any case, with the new My Sky at Night webpage you can generate maps for your own city, which will make it easier to find a location closer to where you live.