It's based on unique visitors & them playing the tracks. I have the VIP premium service on there, for a more "professional" look. I've hit the number 1 spot in various genre's on there before, and it was because of me going out and advertising. For me, it's more of a "drive", since there's no way in hell with the amount of advertising $$ I have, can get one track up the soundscan to compete with those people on the top 10 of the billboards. SO, I tend to keep on advertising, gaining more listeners, in turn, appear on the first page of that genre, or some where close to it.
Frankly, there is a LOT of artists on soundclick, BUT, you gotta basically cut some of those number's in half (those who are at the very bottom of the list on the charts that haven't been on there for years). There are a lot of artists who are active in the soundclick community, but there are also a lot of junk artists who haven't touched their account for a long while. Anyways...
The reason why those people stay on the top, is because of advertising tricks etc... And friend who come on there and play a track for them, and MOSTLY they go on other people's sound click sites, and post up on their message board something like "Hey nice track, why don't you come and play mine", and the fools go and play their track because they think they played theirs. The most hardest charts on there to get to the top is the hip hop general charts. Those are full of active users, who are in a constant battle of marketing to hit the top. WHICH is a good thing btw, getting your music heard and all. It's actually helpful to those who are willing to do what it takes to get their music heard.
Also...no matter how some people look at it, there is some truth in these charts, just like the billboard charts... back in the day, soundclick allowed just any amount of plays, and it hit number one, which means you could have 5 computers at your house, playing the same track over and over again, and hit number 1 easily. They then changed it to unique visitors, which means that the person listening is well, been to your site once that day and played a track (Even if they come 10 times and played the same track during the day), only 1 is really counted towards the charts etc. That's the number that you really should be looking at. The higher that number, the better your music is being heard... ALSO, being on the top 40 or so, there's ALOT more people that come in and listen... Look at yourself for example... They did all the marketing to enter the top 10 right??? And you wondering why they are in the top 10 etc, curious to what kind of music they have, come into their site, and play a track from them, yourself. That gives them more points on the charts. That means you listened to their music, that means they got heard. Keep at it, it's not a scam lol think of it as useful tools