TopoJSON Merger

Combine multiple TopoJSON files into a single Topology. All processing happens in your browser — no uploads, completely private.

How it works

This tool merges multiple TopoJSON files by combining their objects and arcs into a single Topology. You can select which properties to include in the merged output. Perfect for combining regional datasets or consolidating map data from multiple sources.

How to merge TopoJSON files

1. Upload files — Click "Browse Files" or drag-and-drop multiple .topojson/.json files
2. Review files — Check file sizes, object counts, and fix any parse errors
3. Select properties — Choose which properties to keep using checkboxes, or click "Common Only" to include only properties present in all files
4. Preview — View the merged result on an interactive map
5. Download — Get your merged topology as a single .topojson file

Features

• ✅ Merge multiple TopoJSON files — Combine Topologies from different sources
• ✅ Property selection — Choose which properties to include with checkboxes
• ✅ Quick actions — Select All, Deselect All, or Common Only
• ✅ Map preview — See merged geometry on an interactive Leaflet map
• ✅ Batch operations — Undo last add, remove errors, clear all
• ✅ Size statistics — Input size, output size, and object counts
• ✅ 100% client-side — No uploads, works offline after page load

Use cases

• 📍 Combine regional maps — Merge state/province TopoJSON files into a country map
• 📍 Consolidate datasets — Combine historical and current boundary data
• 📍 Data preparation — Merge multiple sources before further processing
• 📍 Reduce file count — Combine many small files into one manageable file
• 📍 Property management — Select only the properties you need from multiple files

Tips

• Arc topology preserved — TopoJSON's arc-sharing structure is maintained
• Large datasets — Preview samples first 1000 features for performance
• Property intersection — Use "Common Only" to keep only shared properties
• Optimize after merge — Use TopoJSON Minifier to reduce file size
• Convert if needed — Convert to GeoJSON first with converters if mixing formats

Technical details

Input format

• TopoJSON Topology — Standard TopoJSON format with type: "Topology"
• Objects — All objects from input files are combined
• Arcs — Arc arrays are concatenated and indices adjusted
• Properties — User-selectable property inclusion

Output format

• Single Topology — One TopoJSON file with all objects merged
• Preserved structure — Arc topology and quantization maintained
• Selected properties — Only chosen properties included in output

Privacy

Everything runs in your browser. Files are not uploaded to any server. After the page loads, the tool works offline.

Related tools

• GeoJSON Merger — Merge GeoJSON files
• TopoJSON Minifier — Optimize TopoJSON file size
• GeoJSON to TopoJSON Converter — Convert between formats
• GeoJSON Minifier — Optimize GeoJSON files

FAQ

Can I merge GeoJSON and TopoJSON together? No, you need to convert them to the same format first. Use the converters to convert GeoJSON to TopoJSON or vice versa.

What happens to the arcs? All arcs from input files are concatenated, and arc indices in geometries are adjusted to reference the correct positions in the merged arc array.

Does it preserve topology? Yes, the arc-sharing structure of TopoJSON is preserved. Shared boundaries remain shared in the output.

How are properties handled? You choose which properties to include via checkboxes. By default all properties are included. Use "Common Only" to keep only properties present in all files.

Can I merge files with different quantization? Yes, but be aware that quantization settings from the first file will be used for the merged output.