Grid2Poster, released by Open Energy Transition, is a Python tool that generates print-ready cartographic posters of electrical transmission infrastructure by querying OpenStreetMap and rendering the results through GeoPandas, OSMnx, and Matplotlib. The project sits at an intersection that rarely gets serious attention: the boundary between open geospatial data pipelines and the kind of infrastructure visualisation work that has historically required proprietary GIS tooling or direct access to grid operator datasets. It is worth examining both what the tool does well and where its constraints reflect deeper tensions in the open energy data ecosystem.
Architecture and Data Pipeline
The core pipeline is straightforward. Given a country name or a GeoJSON boundary file, the tool resolves a geographic boundary either through Nominatim geocoding or the Natural Earth admin-0 dataset for continent-level queries. It then tiles that boundary and issues a series of Overpass API queries to retrieve OSM features tagged as power=line, optionally supplemented by power=minor_line and power=cable. Retrieved geometries are cached locally to avoid redundant network requests, then projected, filtered, and rendered through Matplotlib with configurable themes.
The tiling strategy is a practical necessity. Overpass imposes per-query size limits, and a naive bounding-box query over a large country will either time out or be rejected. The --tile-size-km parameter controls the tile footprint; the default of 200 km works for most mid-sized countries, but continent-scale runs at 500 km can still take several hours. This is an inherent limitation of pulling live data from a community-maintained API rather than a pre-processed bulk export, and it is worth noting that OSM's planet.osm extracts or regional Geofabrik snapshots could in principle be used to build a much faster offline variant.
The projection default of EPSG:3857 (Web Mercator) is pragmatic for country-level posters but introduces well-known area distortion at high latitudes. For a poster of Scandinavia or Canada, a national-grid or azimuthal equidistant projection would preserve shape more faithfully. The --crs flag allows overriding this, which is a sensible design choice, though the documentation does not guide users toward projection selection in any depth.
OpenStreetMap as Infrastructure Data Source
The most significant methodological question the project raises is the reliability of OSM as a source for transmission infrastructure. OSM coverage of high-voltage transmission lines is genuinely good in Western Europe, North America, and parts of East Asia, where active mapping communities have traced lines from satellite imagery and cross-referenced with publicly available grid data. Outside these regions, coverage degrades substantially and unevenly.
The project acknowledges this directly and points users toward MapYourGrid, a community initiative coordinating transmission infrastructure mapping. This is the right response, but it also highlights a circularity: the tool's utility is contingent on the very data quality it is trying to visualise. A poster of Germany will be a reasonably accurate representation of the transmission network. A poster of, say, the Democratic Republic of Congo may omit large portions of the actual grid simply because they have not yet been traced in OSM.
For research applications, this matters considerably. Academic work in energy systems modelling, such as PyPSA-based studies of grid expansion or renewable integration, has grappled with the same data quality problem. Projects like the Global Electricity Network Inventory (GENI) and the work underpinning PyPSA-Earth have invested significant effort in cleaning and validating OSM power data specifically because the raw tag coverage is inconsistent. Grid2Poster inherits all of that underlying uncertainty without, in its current form, surfacing any quality metadata to the end user. A completeness indicator per country, perhaps drawn from MapYourGrid's statistics, would make the tool considerably more honest about what it is showing.
Cartographic Design and Theming
The theming system is one of the more thoughtful aspects of the implementation. Themes are defined as JSON files in a themes/ directory, which means users can extend the system without touching Python code. The shipped themes cover a reasonable range of aesthetics, from the understated paper_grid to the high-contrast neon_cyberpunk, and the gallery in the README demonstrates that the output is genuinely attractive across a variety of countries and regions.
The project draws explicit inspiration from maptoposter and similar cartographic poster projects that have become popular in the OSM community. This lineage is worth acknowledging because it situates Grid2Poster within a broader trend of using open geospatial data for aesthetic outputs rather than purely analytical ones. The tension between accuracy and visual appeal is real: a neon_cyberpunk theme applied to an incomplete dataset produces a striking image that may convey false confidence about infrastructure coverage.
The SVG output is particularly valuable. Unlike rasterised PNG output, SVG preserves the geometric structure of the rendered lines, making it suitable for further editing in Inkscape or Illustrator, or for use in web applications where the grid topology could be made interactive. The --export-geojson flag, which writes all retrieved transmission lines as a WGS84 GeoJSON file, extends this further and turns the tool into a lightweight data acquisition pipeline in its own right.
Predefined Regions and Synchronous Area Boundaries
The bundled regional GeoJSON files deserve specific attention. The continental_europe.geojson boundary, for instance, encodes the Continental European Synchronous Area as it stood after the Baltic states synchronised in February 2025. This is a technically precise choice that reflects actual grid interconnection topology rather than political geography. The distinction matters: Norway and Sweden are excluded not because they are not European but because they operate in the Nordic synchronous area and are not AC-coupled to the Continental European grid.
This kind of domain-specific boundary definition is genuinely useful and not trivial to get right. The inclusion of Moldova and Ukraine, which synchronised with Continental Europe in March 2022 following the Russian invasion, is current and accurate. These predefined regions suggest that at least some contributors have energy systems domain knowledge, not just geospatial programming expertise, and that is a meaningful differentiator from generic mapping tools.
Other predefined regions, such as MENA and Southeast Asia, follow political rather than electrical groupings, which is a reasonable fallback where synchronous area boundaries do not map cleanly onto recognisable geographic regions. A future extension that encoded ENTSO-E synchronous area boundaries, the Southern African Power Pool footprint, or the GCC Interconnection Authority region would make the tool more analytically useful for grid researchers.
Limitations and Research Directions
Several limitations are worth summarising for anyone considering the tool for research use:
- No voltage stratification by default. Transmission lines in OSM carry
voltagetags where mappers have recorded them, but Grid2Poster does not currently appear to filter or style by voltage level. Rendering 400 kV backbone lines identically to 110 kV regional lines obscures the hierarchical structure of the network, which is analytically significant. - No topological validation. The tool renders geometries but does not construct or validate a graph. Disconnected line segments, common in OSM due to incomplete tracing, will appear visually continuous but are not electrically connected. For any application beyond poster generation, a topology-aware post-processing step is necessary.
- Overpass dependency. Live querying of Overpass introduces rate-limiting, latency, and reproducibility concerns. A workflow based on versioned OSM extracts would be more suitable for research that requires consistent inputs across runs.
- No substation rendering. Transmission lines without substations present an incomplete picture of grid infrastructure. Substations are the nodes that define the electrical topology; their absence means the posters are aesthetically closer to circuit diagrams without nodes than to actual grid maps.
None of these are criticisms of the project as a poster-generation tool. They are relevant only if one attempts to extend its use into analytical territory.
As open energy data becomes increasingly central to grid planning, renewable integration studies, and climate policy modelling, tools that lower the barrier to visualising and working with infrastructure data have real value. Grid2Poster contributes to that ecosystem in a way that is accessible, visually compelling, and grounded in a legitimate open data source. The MapYourGrid initiative it supports is arguably more impactful in the long run: better OSM coverage of transmission infrastructure benefits not just poster generators but every downstream application that depends on open grid data, from PyPSA-Earth to academic network flow models. Contributing accurate transmission line traces to OSM is, in a quiet way, a form of open science infrastructure work.