Let's pretend that a person is doing an ethnographic study on "Social Media Usage", and they find out that a certain percentage of people use Facebook, and another percentage use Twitter, and another uses Instagram. Ok, that's all very useful and interesting information, but how do you get MORE out of this data? Is there anything that ties these groups together? In other words, how can we think about these separate groups as a "logical whole"? Perhaps chronology? When we made our initial discovery about the percentage of people in Facebook/Twitter/Instagram, did we also collect the ages of these people? Can we conclude that people start their "Social Media Usage" on Facebook, and then move to Twitter, and finally end up on Instagram? "Logical whole" simply means you are looking at data that appears to be unconnected, and you are trying to find a way to connect them by stepping back and looking at the bigger picture.

A bit of tricky question in some senses actually, especially without reading more about what the ethnographical study was regarding more specifically. To combine things into a "logical whole" would seem to refer to the grouping together of similar/related data got from the study; so his example of chronology means that they group information and put it on a timeline. I hope that kind of answers your question at least.