In projects related to urban development, business analytics, and GIS, the same question arises again and again: how accessible is an area in real life, not just on a map? Isochrones provide one of the most visual answers. They allow us to evaluate space using travel time rather than abstract distances.

What are isochrones and why are they needed?

Isochrones are lines on a map connecting points that can be reached in the same amount of time from a given starting point. They are used to visualize transportation accessibility and estimate travel times.

Types of isochrones:

Pedestrian isochrones – show how long it takes to walk.
Automotive isochrones – take into account road conditions, speed limits, and traffic jams.
Public transportation isochrones – model travel times based on transportation schedules.
Bicycle isochrones – take into account terrain and available bike paths.

Unlike conventional buffers, isochrones take into account the actual transportation network – roads, routes, restrictions, and travel speeds. This is why they are widely used in urban development, transportation planning, and retail.

From the First Isochrone Maps to Modern GIS

The concept of isochrones emerged long before the advent of digital cartography. The first isochrone maps appeared in the 19th century and were created entirely in analog format. They were hand-drawn on paper maps, showing areas accessible by foot, horseback, or rail in a given time.

Isochrone map of Paris, 1882

Calculations were based on average speeds and simplified assumptions about routes and terrain. Despite their low accuracy by modern standards, they were widely used in military planning, postal logistics, and early urban studies.

With the development of computing technology and GIS, isochrones moved from static paper maps to digital vector formats. Hand-drawn contours gave way to lines and polygons, and network analysis made it possible to take into account real-world transportation infrastructure. Today, isochrones exist as dynamic vector layers that are calculated and visualized interactively in desktop and web GIS.

How are isochrones constructed in GIS?

Isochrone construction is based on network analysis. The transportation network is represented as a graph, where each segment is assigned a value—time or distance. Routing algorithms determine which parts of the network are reachable within a given threshold, after which the results are visualized as availability zones.

In most cases, OpenStreetMap is used as the underlying network. Depending on the tool, different types of transportation, speed profiles, and traffic restrictions may be taken into account.

How are isochrones constructed in QGIS?

Desktop GIS, such as QGIS, offer several ways to construct isochrones using network analysis tools and various plugins. One of the most popular solutions is QNEAT3 (QGIS Network Analysis Toolbox). This plugin allows you to construct isochrones based on a road network based on time or distance. QNEAT3 uses graph algorithms and is suitable for detailed spatial analysis, but requires a properly prepared network and velocity or weight attributes.

Another popular option is ORS Tools, which connects QGIS to the OpenRouteService API. It allows for quick isochrone construction without manual network preparation, but depends on the external service, API limits, and available routing profiles.

QGIS also offers built-in network analysis tools for calculating service and reachability areas. These tools are powerful, but less intuitive and often require multiple processing steps.

Isochrones on GISCARTA: Transportation Accessibility Widget

On the GISCARTA platform, we've implemented isochrone calculation in the form of a transportation accessibility widget.

On our GIS platform, accessibility analysis is implemented through a dedicated transport accessibility widget designed for everyday analytical and presentation tasks.

Shortest route calculation
Users can build the shortest route between two or more points directly on the map. The route is calculated along the transport network and adapts to the selected mode of movement, allowing quick comparison of travel options and distances.

Build the shortest route on the platform GISCARTA using the Transport Accessibility widget.

Isochrones from one or multiple locations

The widget allows building isochrones from a single point or from multiple starting points at once. This makes it possible to compare accessibility from different locations and visually assess overlapping or competing service areas.

For both routing and isochrones, users can choose the mode of transport:
– pedestrian access;
– bicycle routing;
– car travel.

Depending on the selected mode, the widget automatically applies different routing profiles and movement assumptions. Isochrones are generated for selected time intervals and displayed as clear, layered zones on the map.

This approach makes it easy to answer practical questions such as:
– which areas are reachable within a given time;
– how accessibility changes between transport modes;
– where service areas intersect or differ.

The widget is designed to work without data preparation or GIS configuration. All calculations are performed in the background, allowing users to focus on interpretation rather than technical setup.

Building isochrones on the platform GISCARTA using the Transport Accessibility widget.

Key takeaways

Isochrones shift spatial analysis from abstract distance to real travel time, making accessibility easier to interpret and communicate.
The accuracy of isochrones strongly depends on the quality of the underlying transport network and routing assumptions.
Desktop GIS tools like QGIS provide powerful and flexible isochrone workflows, but require data preparation and technical expertise.
Web-based isochrones prioritize speed, interactivity, and clarity, making them especially effective for exploratory analysis and decision-making.

FAQ

What are isochrones mainly used for?
Isochrones are used to analyze transport accessibility in urban planning, business location analysis, logistics, and social infrastructure studies.

How are isochrones different from buffers?
Buffers are based on straight-line distance, while isochrones rely on transport networks and travel time, producing more realistic results.

Can isochrones be built using open data?
Yes. Most modern isochrone tools use open transport data, primarily OpenStreetMap, combined with routing algorithms.

When should QGIS be used instead of web-based tools?
QGIS is preferable for advanced analysis, custom workflows, and research tasks that require full control over data and parameters.