This example displays two time-series line charts of water level data from wells OW2DWL and OW2DSWL, with an orange and blue color legend. The lower chart supports brush-based selection, which filters the upper chart’s time range and overlays a dashed grey trend line computed via least-squares regression. The visualization uses D3 v5 APIs including `scaleTime`, `scaleLinear`, `scaleOrdinal`, `line`, `nest`, `brushX`, and `axisBottom`, rendering to SVG.