Upload an Excel spreadsheet containing latitude, longitude and a numeric value, then generate a smooth, colour-graded heat map showing how that value is distributed across the map. Customise the colour gradient, smoothing power and resolution, then export the result as an image. Open full screen ↗
Turn a Spreadsheet Into a Spatial Picture
A table of numbers is hard to read at a glance — a map is not. This tool takes any Excel spreadsheet with a latitude column, a longitude column, and any numeric value column (population, sales, temperature, survey scores, anything), and interpolates a smooth, continuous heat map showing how that value varies across the region, even between the points you actually measured.
Step-by-Step Guide
Step 1
Open the tool
The map loads centred on the world with an empty state. Upload File, Load Sample, Generate Heatmap and Clear controls sit in the floating toolbar; the sidebar holds column selection, gradient styling and export options.
Step 2
Upload an Excel or CSV file
Click "Upload File" and choose an .xlsx, .xls or .csv file, or click "Load Sample" to try 30 US cities by population instantly.
Step 3
Confirm the data columns
Latitude, longitude and value columns are auto-detected where possible. Check the sidebar dropdowns and correct any that were guessed wrong.
Step 4
Generate the heat map
Click "Generate Heatmap". The map zooms to fit your data's extent and renders the interpolated colour surface.
Step 5
Adjust the colour gradient
Change the Low, Mid and High colours to match your presentation, or use the default green-to-red intensity scale.
Step 6
Fine-tune power and resolution
Raise the Power slider for sharper, more localised hot spots, or lower it for smoother blending. Increase Resolution for a crisper gradient.
Step 7
Pan and zoom to explore
The heat map automatically re-renders as you pan or zoom, always fitting the current view.
Step 8
Export the result
Click "Download Heatmap (PNG)" to save a combined basemap-and-heatmap image for reports or presentations.
Frequently Asked Questions
What does the Power setting actually change?
It controls how quickly a point's influence fades with distance. Higher power values make the heat map look more like isolated 'bullseyes' around each point; lower values blend everything into smoother, more gradual gradients.
How is this different from just plotting points on a map?
Plotting points shows you exactly where your measurements were taken. A heat map goes further, estimating the value everywhere in between, so you can see continuous patterns and hot spots rather than isolated dots.
What is IDW interpolation?
Inverse Distance Weighting is a method for estimating values at unmeasured locations by averaging nearby known values, weighted so that closer points count more than distant ones. It's one of the most widely used spatial interpolation techniques in GIS.
How many rows can I upload?
Up to 5,000 rows. Larger files are trimmed to the first 5,000 rows, with a notice shown so you're aware.
Why did my heatmap only cover part of the map?
The heat map is clipped to the convex hull of your data points — the tightest boundary enclosing all of them — rather than a rectangle, so it never extends into areas far from any of your points. If your points cluster in one region, the coloured area will follow that region's outline — this is expected, not a bug.
Why does the export sometimes only include the heat map, not the basemap?
Some tile servers restrict cross-origin image reads for security reasons, which can prevent combining the basemap into the exported image. When that happens, the tool automatically falls back to exporting just the heat map layer with a transparent background.
What file formats does the tool accept?
Excel workbooks (.xlsx and the older .xls format) and plain .csv files are all supported, read directly in your browser. Your file needs a latitude column, a longitude column, and at least one numeric column to visualise.
Is my Excel data uploaded to a server?
No. The file is read and parsed entirely in your browser using client-side JavaScript. Nothing is sent to or stored on any server, which makes this tool safe for sensitive or private data.
Can I change the colours after generating the heat map?
Yes. Colour, opacity, power and resolution all apply live to the heat map already on screen — there's no need to regenerate it after a style change.
Can I use a CSV file instead of Excel?
Yes. Click "Upload File" and choose a .csv file — it's read the same way as an Excel workbook, with the same auto-detection of latitude, longitude and value columns.
Watch: Heat Map Generator in Under a Minute
Prefer to watch instead of read? This short walkthrough covers uploading a spreadsheet, mapping its columns, and generating an interactive heat map.
Exporting Your Heat Map
Click "Download Heatmap (PNG)" to save an image combining the basemap and the heat map overlay together, ready to drop into a report or presentation. If the basemap tiles can't be captured due to the tile server's security policy, the tool automatically falls back to exporting just the heat map layer on its own.
Common Use Cases
📈
Sales & Business Analytics
Map sales figures, customer density or revenue by region to spot growth opportunities and gaps.
🏘️
Real Estate & Site Selection
Map property prices, foot traffic or demand scores to identify hot and cold zones.
🌡️
Environmental Monitoring
Interpolate temperature, air quality, rainfall or pollution readings between monitoring stations.
🎓
Academic & Survey Research
Turn any georeferenced survey dataset into a publication-ready spatial visualisation.
👥
Population & Demographics
Visualise population density or demographic concentration across cities, regions or countries.
🏥
Public Health
Visualise case counts, survey results or health indicators across a region from spreadsheet data.
Styling the Heat Map
Three controls in the sidebar shape how the heat map reads:
- Colour Gradient: set the Low, Mid and High colours — the default green-to-red mimics a classic risk/intensity scale, but any three colours work.
- Opacity: from a subtle 20% wash to a fully solid 100% fill.
- Power & Resolution: control how sharply values blend between points, and how fine the rendering grid is.
Every change re-renders the heat map instantly using your already-loaded data — no need to re-upload or regenerate.
How IDW Interpolation Works
The tool uses Inverse Distance Weighting (IDW), a well-established spatial interpolation method: to estimate the value at any location, it takes a weighted average of every known data point, giving more influence to points that are closer and less to points further away.
The Power Setting
The Power slider controls how quickly that influence fades with distance. A low power (close to 1) blends values smoothly over a wide area; a high power (close to 4) makes each data point dominate its immediate surroundings more sharply, producing more localised, less-blended contours.
Resolution vs. Performance
Resolution controls the size of the grid used to compute the interpolation — Low is fastest, Very High produces the smoothest gradient but takes longer to render, especially with many data points. Start with Medium and increase it once you're happy with your column selection and colours.
Clipped to Your Data's Shape
The coloured fill is clipped to the convex hull of your points — the tightest boundary that encloses all of them — rather than a rectangle. A thin dashed outline marks this boundary on the map, so the heat map never bleeds into empty corners far from any point you actually have data for.
Preparing Your Excel or CSV File
Your spreadsheet needs three things, in any column order:
- A latitude column: decimal degrees, e.g. 40.7128.
- A longitude column: decimal degrees, e.g. -74.0060.
- A numeric value column: whatever you want to visualise — population, sales, temperature, a survey score, anything numeric.
Upload the file, confirm (or correct) the three column selections in the sidebar, then click "Generate Heatmap". The map zooms to fit your data and renders the interpolated surface.
Related Tools
Map tiles © OpenStreetMap contributors and Protomaps (hosted by KONAKTIVE), CARTO, Esri (satellite). Excel parsing powered by SheetJS. Map rendering by Leaflet. All parsing and interpolation is computed locally in your browser — no data is uploaded to any server.
