Free Online Contour Map Generator: XYZ Data to Contour Map

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Click anywhere on the map to read the interpolated value at that spot. The demo data is a surveyed hill with a basin beside it; replace it with your own elevations, water levels, formation tops, or grades.

From a list of numbers to a finished map

Every field science eventually produces the same humble file: three columns of x, y, and a value. Elevations from a topo survey, water levels from monitoring wells, formation tops from drilling, grades from sampling. The app above turns that file into a finished contour map in one click. Paste the points or load a CSV, and it grids them with inverse distance weighting, colors the surface, threads labeled contour lines through it with the marching squares algorithm, and overlays your data points. Click anywhere to read the interpolated value. Download the map as a PNG or print a report.

Scattered survey points over a colored contour map with a green hill and blue basin, showing how inverse distance weighting and marching squares turn XYZ data into contours
Inverse distance weighting fills the grid from your points; marching squares threads the contour lines through it.

This is the first app in the Maps and Sections Suite, the mapping wing of the site, and it consumes the numbers that many of the calculators here produce: elevation grids from earthworks, water levels from pumping tests, grades from assay compositing.

What the two algorithms do

  • Inverse distance weighting estimates each grid cell by asking every survey point for its opinion, trusting near points far more than distant ones; the power setting controls how fast that trust decays, with 2 the standard and higher values honoring local data more tightly.
  • Marching squares walks the grid cell by cell and finds exactly where each contour level crosses the cell edges, which is why the lines pass precisely between your points instead of through them.
  • The auto interval picks a clean round number giving about ten contours; set your own for survey-standard intervals like 0.5 m water table maps or 5 m topo.
  • Grid resolution trades smoothness for speed: 120 cells is crisp for most datasets, and a few hundred points still map instantly.

What to map with it

  • Structure contour maps from formation top picks, the geologist's bread and butter.
  • Water table and drawdown maps from monitoring well levels, in the blue ramp.
  • Grade heat maps from drillhole or soil sampling, in the thermal ramp.
  • Site grading and topo from any leveling survey, ready for the earthworks calculator next door.

Honest limits

IDW is the workhorse of quick mapping, but it never extrapolates beyond your data range and it makes bulls-eyes around isolated extreme points; kriging and spline methods in GIS packages smooth those artifacts at the cost of setup time. For a first map, a check on a consultant's figure, or a classroom, this is the same mathematics running instantly and free.

Related Calculators and Reference

Common Questions

How do I make a contour map from XYZ data?

Paste your points as x, y, value rows or load a CSV into the generator at the top of this page, and it grids them with inverse distance weighting and draws labeled contours instantly. The map downloads as a PNG or prints to PDF.

What interpolation does the contour map generator use?

Inverse distance weighting with an adjustable power, followed by marching squares to thread the contour lines through the grid. Power 2 is the standard; higher values honor local points more tightly.

Is my survey data uploaded anywhere?

No. The gridding and drawing happen entirely in your browser, so the data never leaves your machine.