In the US we have Compete, Alexa, and SimilarWeb with self-service interfaces, and Comscore, Nielsen, Experian and others with an enterprise focus. We also have Moz, Wordstream, SEMrush, etc. in the SEO/SEM space.
What's the lay of the land in China? What are the companies that are analogous to these and the overall state of the digital market data ecosystem over there?
In China there is not much.And most of them did the work of reselling/localizing the US stuff into China,such as Alexa,PR.
But nonetheless,here's a short list:
http://www.aizhan.com it monitors Baidu rankings,index and stuff.
http://www.chinaz.com tools and articles about SEO and SEM.
http://www.cnzz.com website statistics and not so much analytics
http://shu.taobao.com consumption indecies offered by Taobao
Hi — the lay of the land (as you put it) in China is very different to the rest of the world. For example, many services we are used to (e.g. Google Analytics) don't work (or doesn't work reliably) within China. This is due to the great firewall the government operates to censor internet content. This also means that things like Alexa, SEO, etc. takes a different form.
The best way is to partner with a local Chinese digital agency. There are several boutique agencies who have existing branches in Europe/US for this reason.
Let me know if you want some intros.