We investigate regions formed by cylinders of circles of fixed radii. We investigate graphs obtained by collapsing each level set of the functions represented by the natural projections of them to the $1$-dimensional line. Some specific trees obtained in simple ways from so-called balanced trees are shown to be realized as such graphs. Related studies on regions in the Euclidean plane surrounded by real algebraic curves are presented by several researchers. One of pioneering studies is presented by Bodin, Popescu-Pampu and Sorea in 2022--3 as an elementary and surprisingly new study. The author has been interested in related studies and also in constructing natural and explicit real algebraic maps onto such regions, generalizing the canonical projections of the unit spheres. Such studies in real algebraic geometry, different from theory of existence in the last century, mainly studied by Nash and Tognoli, are remarked.