The quartile ranking method used for journals is based on the Impact Factors (IF) of publications from Science Citation Index (SCI) database. This ranking is published by the Journal Citation Reports (JCR) every year.
In which, Q1 denotes the top 25% of the IF distribution, Q2 for middle-high position (between top 50% and top 25%), Q3 middle-low position (top 75% to top 50%), and Q4the lowest position (bottom 25% of the IF distribution).
There has also been some related questions at Research gate :
There are some conferences when they accept the papers, they are published in a proceeding book or in a journal, while there are other conferences that allow the authors to present their papers but do not publish them
Please note that a conference paper is different, considerably, from a journal paper in view of format and content. Each journal can have its own policy in this regard. But it's very common that conferences agree with one or more journals to recommend their top papers to them. In this case, the papers should be extended and the other criteria of the journals should be respected. The editors are more likely to evaluate the papers according to their own peer-review system. At the time of publishing, it must also be noted, in final version, that a part of this paper, entitled X, is presented at the Y conference on Z date.