What is a cryptocurrency bubble map?

Could you please elaborate on what a cryptocurrency bubble map actually is? As an expert in the field of cryptocurrency and finance, I'm interested in understanding the significance and methodology behind such a visual representation. Is it a way to identify overvalued or undervalued cryptos? How is the data collated and interpreted to form this bubble map? And furthermore, what role does it play in making informed investment decisions? Clarifying these aspects would be extremely valuable for those seeking to navigate the volatile world of cryptocurrencies.