after compiling a considerable number of physical and observational properties of these objects, particularly their degree of correlation with the surrounding molecular environment, if present. We take advantage of the recently completed ATLASGAL submm continuum survey (see Section \[sec:galactic-surveys\]), which provides a spatially unbiased view of the distribution of the dense molecular material in the Milky Way. While the distinction of ECs from OCs in these catalogs has primarily been made via correlations with known regions or nebulae seen in the infrared, the ATLASGAL survey allows us to objectively tell[^2] whether or not these objects are associated with dense molecular gas, as well as to possibly detect the presence of stellar feedback via simple morphological criteria.

This paper is organized as follows. In the remainder of this introduction, we shortly present the main observational data and the nomenclature used throughout this work (Sections \[sec:galactic-surveys\] and \[sec:cluster-definition\], respectively). In Section \[sec:catalogs-summary\], we describe the literature compilation of a merged list of Galactic OCs and ECs, including a new search for ECs we conducted on the GLIMPSE survey; more details about the literature cluster lists used here are given in Appendix \[sec:catalogs-long\]. Section \[sec:huge-table\] summarizes the construction of an extensive catalog for 