it's obvious they are cherry-picking data, omitting many dozens of exchanges and markets. the idea that ETH has a deeper market than BTC is completely laughable. and they're saying that XRP has 91% of the market depth of BTC? over the top ridiculous.
also, basing this type of assessment on order books alone is neglecting to account for all OTC and p2p trading.
They seem to be displaying the rank of the coins based on the buy pressure. If you click on an individual coin, you can see the sources of data from the exchanges that they're on from the chart at the bottom of the page. The site seems to be polling data from the exchanges, as the exchange prices are reflected on the coin's page.
I gather, from your responses, that when you all are trading, that you look at the market cap data vs. market depth data? Is this an accurate assessment? I'm not a trader, so I'm just trying to figure out what is the most important factor when considering a high-volume trade.