ggplot2</strong> data structures and not the result of custom geoms.<a href="#fn9" class="footnote-ref" id="fnref9"><sup>9</sup></a> Some great examples of R packages that extend <strong>ggplot2</strong> using core data structures are <strong>ggforce</strong>, <strong>naniar</strong>, and <strong>GGally</strong> <span class="citation">(Pedersen <a href="#ref-ggforce" role="doc-biblioref">2019</a>; Tierney et al. <a href="#ref-naniar" role="doc-biblioref">2018</a>; Schloerke et al. <a href="#ref-GGally" role