Free Online Cross Section Maker: Geological Section from Boreholes

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Layers with the same unit at the same position in adjacent holes are correlated and filled between them; where the sequences differ the section leaves an honest gap. Enter each hole's distance along the section line, collar elevation, water table depth, and layer bottoms. Leave a hole's distance blank to skip it.

From four logs to one picture of the ground

A boring log knows one point; a cross section claims the ground in between, which is where foundations, tunnels, and water actually are. The app above draws that claim. Enter up to four boreholes with their distance along the section line, collar elevation, water table depth, and layer bottoms, and it renders a scaled geological section: colored borehole strips, correlated layers filled between holes, the ground surface, the water table dashed in blue, elevation axes, and a legend. Vertical exaggeration is adjustable and reported honestly. Export the drawing as a PNG or print a report.

Geological cross section with three boreholes correlated into sand, clay, and bedrock layers under a ground surface line, with the water table dashed in blue
Correlate the same layers between holes and the ground between them stops being a guess.

This is the second app in the Maps and Sections Suite, and the natural next step from the borehole log creator in the site investigation suite: log the holes there, correlate them here.

How the correlation works

  • Layers are matched by unit and position: the second layer in BH-1 correlates with the second layer in BH-2 only when both are the same unit, which is the standard first-pass assumption of layer-cake stratigraphy.
  • Where the sequences differ, the section leaves a gap instead of inventing geology; a pinching-out layer or a fault shows up as exactly that honest blank.
  • Boundaries between holes are straight lines, the simplest defensible interpolation; the real surface wiggles, but no drawing method knows how without more holes.
  • Vertical exaggeration makes thin layers visible on long sections; the app reports the actual exaggeration used so nobody mistakes a 5x drawing for true scale.

What to use it for

  • Site investigation reporting: the section is the figure every geotechnical report is built around.
  • Teaching correlation: change one layer in one hole and watch the picture react.
  • Groundwater studies: the dashed water table across a section shows gradients that single logs hide.
  • Quick checks of a consultant's drawn section against the raw log depths.

Honest limits

Real correlation uses judgment this app cannot have: lithology can repeat, units pinch out, and faults offset sequences. Treat the automatic match as the starting hypothesis it is, exactly as a geologist does with a first pencil draft. For sections with dozens of holes and interpretive control, dedicated packages take over; for the four-hole sections that dominate real site work, this does the job in a browser tab.

Related Calculators and Reference

Common Questions

How do you draw a geological cross section from boreholes?

Plot each hole at its distance along the section line with its collar elevation, mark the layer boundaries at their true elevations, and connect matching layers between holes. The tool on this page does all of it and prints the result.

What is vertical exaggeration?

The vertical scale divided by the horizontal scale. Sections stretch the vertical so thin layers stay visible on long lines; the tool reports the exaggeration used so nobody mistakes the drawing for true scale.

How are layers correlated between boreholes?

The first pass matches layers by unit and position, the layer cake assumption. Where sequences differ the section leaves a gap, because pinchouts and faults deserve interpretation rather than automatic lines.