topojson-server

What is topojson-server?

The topojson-server npm package is used to convert GeoJSON objects to TopoJSON. TopoJSON is an extension of GeoJSON that encodes topology, which can significantly reduce the size of the data and improve the efficiency of spatial operations.

What are topojson-server's main functionalities?

Convert GeoJSON to TopoJSON

This feature allows you to convert a GeoJSON object into a TopoJSON object. The code sample demonstrates how to use the `topology` function to achieve this conversion.

const topojson = require('topojson-server');
const geojson = { "type": "FeatureCollection", "features": [ { "type": "Feature", "geometry": { "type": "Polygon", "coordinates": [ [ [0, 0], [0, 1], [1, 1], [1, 0], [0, 0] ] ] } } ] };
const topology = topojson.topology({ myGeo: geojson });
console.log(JSON.stringify(topology));

Simplify TopoJSON

This feature allows you to simplify a TopoJSON object, which can be useful for reducing the complexity of the data. The code sample demonstrates how to use the `simplify` function to simplify a TopoJSON object.

const topojson = require('topojson-server');
const geojson = { "type": "FeatureCollection", "features": [ { "type": "Feature", "geometry": { "type": "Polygon", "coordinates": [ [ [0, 0], [0, 1], [1, 1], [1, 0], [0, 0] ] ] } } ] };
const topology = topojson.topology({ myGeo: geojson });
const simplified = topojson.simplify(topology, 0.01);
console.log(JSON.stringify(simplified));

Quantize TopoJSON

This feature allows you to quantize a TopoJSON object, which can help in reducing the file size by limiting the precision of the coordinates. The code sample demonstrates how to use the `quantize` function to quantize a TopoJSON object.

const topojson = require('topojson-server');
const geojson = { "type": "FeatureCollection", "features": [ { "type": "Feature", "geometry": { "type": "Polygon", "coordinates": [ [ [0, 0], [0, 1], [1, 1], [1, 0], [0, 0] ] ] } } ] };
const topology = topojson.topology({ myGeo: geojson });
const quantized = topojson.quantize(topology, 1e4);
console.log(JSON.stringify(quantized));

Other packages similar to topojson-server

geojson

The geojson package provides utilities for working with GeoJSON data. While it does not support TopoJSON, it offers a range of functions for manipulating GeoJSON objects, such as validation, bounding box calculation, and more.

mapshaper

Mapshaper is a tool for editing Shapefile, GeoJSON, TopoJSON, and other map formats. It offers a command-line interface and a web-based interface for simplifying, filtering, and converting map data. Compared to topojson-server, Mapshaper provides a broader range of data manipulation features.

shapefile

The shapefile package is used for reading and writing Shapefiles, which are a popular format for geographic data. While it does not directly support TopoJSON, it can be used in conjunction with other tools to convert Shapefiles to GeoJSON and then to TopoJSON.

README

TopoJSON Server

The topojson-server module provides tools for converting GeoJSON to TopoJSON. See How to Infer Topology for details on how the topology is constructed.

See shapefile for converting ESRI shapefiles to GeoJSON, ndjson-cli for manipulating newline-delimited JSON streams, d3-geo-projection for manipulating GeoJSON, and topojson-client for manipulating TopoJSON and converting it back to GeoJSON. See also us-atlas and world-atlas for pre-built TopoJSON.

Installing

If you use NPM, npm install topojson-server. Otherwise, download the latest release. You can also load directly from unpkg. AMD, CommonJS, and vanilla environments are supported. In vanilla, a topojson global is exported:

<script src="https://unpkg.com/topojson-server@3"></script>
<script>

var topology = topojson.topology({foo: geojson});

</script>

Try topojson-server in your browser.

API Reference

# topojson.topology(objects[, quantization]) <>

Returns a TopoJSON topology for the specified GeoJSON objects. The returned topology makes a shallow copy of the input objects: the identifier, bounding box, properties and coordinates of input objects may be shared with the output topology.

If a quantization parameter is specified, the input geometry is quantized prior to computing the topology, the returned topology is quantized, and its arcs are delta-encoded. Quantization is recommended to improve the quality of the topology if the input geometry is messy (i.e., small floating point error means that adjacent boundaries do not have identical values); typical values are powers of ten, such as 1e4, 1e5 or 1e6. See also topojson.quantize to quantize a topology after it has been constructed, without altering the topological relationships.

Command-Line Reference

geo2topo

# geo2topo [options…] [name=]file… <>

Converts one or more GeoJSON objects to an output topology. For example, to convert a GeoJSON FeatureCollection in the input file us-states.json to a TopologyJSON topology in the output file us.json:

geo2topo states=us-states.json > us.json

The resulting topology has a “states” object which corresponds to the input geometry. For convenience, you can omit the object name and specify only the output file name; the object name will then be the basename of the file, with the directory and extension removed. For example, to convert the states.json GeoJSON FeatureCollection to a TopologyJSON topology with the “states” object in us.json:

geo2topo states.json > us.json

Any properties and identifiers of input feature objects are propagated to the output. If you want to transform or filter properties, try ndjson-cli as demonstrated in Command-Line Cartography.

See also topo2geo.

# geo2topo -h
# geo2topo --help

Output usage information.

# geo2topo -V
# geo2topo --version

Output the version number.

# geo2topo -n
# geo2topo --newline-delimited

Accept newline-delimited JSON, with one feature per line.

# geo2topo -o file
# geo2topo --out file

Specify the output TopoJSON file name. Defaults to “-” for stdout.

# geo2topo -q count
# geo2topo --quantization count

Specify a pre-quantization paramter. 0 disables quantization. See topojson.topology for a description of quantization.