Automatic Geological Cross-Section
Draw a line on the map: topographic profile, surface geology, projected dips and a constructed section ready for the report.
Builds a geological cross-section along any line: the topographic profile from a global elevation model, the geological units cut by the line with their exact contacts and ages, strike-and-dip measurements from the field or typed in projected onto the section with their apparent dip, and a subsurface constructed from the contacts by the rule that beds dip towards younger strata. Units, ages and dips can be edited, and the section is drawn as a finished figure with vertical exaggeration, scale and legend.
Overview
A cross-section is part of almost every geological report, field course and thesis, yet it is still drawn by hand: reading contours, transferring contacts with a strip of paper and constructing apparent dips with a protractor. Here the profile, the contacts and the apparent dips are measured exactly, and the geologist’s judgement goes into editing the units and the dips rather than into drafting.
Measurements recorded with the Field Survey Companion are imported in one tap, and the last section is kept on the device so it can be reopened without a connection.
What you enter · What you get
What you enter
- Section line (two points on the map or coordinates)
- Elevation model
- Strike and dip of beds and faults (field, import or typed)
- Projection distance, default dip, depth and vertical exaggeration
What you get
- Topographic profile with length, relief and azimuth
- Geological units along the line with contacts, ages and lithology
- Apparent dips of the projected measurements
- Constructed geological section and its figure
- Tables and exports for GIS and drawing programs
How it works in the field
Method and equations
Profile and contacts
The line is sampled at 600 points; elevations come from the elevation model and units from the geological map polygons that the line crosses, keeping one source map along the whole line where possible so that contacts are not artefacts of joining maps of different scales.
Apparent dip
Measurements within the projection distance are moved perpendicularly onto the line; the dip seen in the section depends on the angle β between the dip direction and the section azimuth, and is steepened on the figure by the vertical exaggeration.
Construction
Each surface contact is projected downward with the apparent dip of the nearest bedding measurement, or with the default dip, towards the younger unit. Going down each vertical of the section, crossing a contact passes into the older unit, which builds a layer-cake interpretation without crossing contacts.
Accuracy and error limits
- The profile is as good as the elevation model (about ±5–10 m vertically with the 30 m models); contacts are as good as the geological map, typically 50–250 m at 1:100 000 and 0.5–2.5 km at 1:1 000 000, so use sections at a scale that suits the source. Apparent dips are exact for the measured planes.
- What is not covered: the subsurface is an interpretation, not data. Folds without measurements on both limbs, unconformities, intrusions, thickness changes and fault displacements are not reconstructed, and faults are drawn without offset. Where the map is a global compilation, small formations may be merged or missing.
- To reduce the error: draw the line perpendicular to strike, take dips on both limbs of folds and near every contact, keep the projection distance small where structure changes along strike, edit unit names and ages from the national geological map, and check the section against wells and the measured thicknesses of formations.
Who uses it
Standards and references
- Ragan, D.M. (2009). Structural Geology: An Introduction to Geometrical Techniques, 4th ed. Cambridge University Press.
- Groshong, R.H. (2006). 3-D Structural Geology: A Practical Guide to Quantitative Surface and Subsurface Map Interpretation, 2nd ed. Springer.
- Lisle, R.J. (2004). Geological Structures and Maps: A Practical Guide, 3rd ed. Elsevier.
- Maltman, A. (1998). Geological Maps: An Introduction, 2nd ed. Wiley.
- Busk, H.G. (1929). Earth Flexures. Cambridge University Press.
- Peters, S.E., Husson, J.M. & Czaplewski, J. (2018). Macrostrat: A platform for geological data integration and deep-time Earth crust research. Geochemistry, Geophysics, Geosystems, 19(4), 1393–1409.
- Jassim, S.Z. & Goff, J.C. (eds.) (2006). Geology of Iraq. Dolin, Prague and Moravian Museum, Brno.
At a glance
- Category
- Field geology
- Runs on
- Phone, tablet and desktop browser
- Export
- Section figure as PNG, JPG and PDF; units and projected measurements as CSV; section line and contacts as GeoJSON and KML; full PDF report
- Access
- Free
Run this survey on your next site
All 64 tools, report export and the AI assistant come with one subscription.