Fetch Basemap

Any dataset with longitude/latitude can sit on a real map with one click. Select a World Grid, press Fetch Basemap… in the World Grid panel, and GlyphViz measures your data's lon/lat bounding box, downloads map imagery for exactly that window from a free map service, and applies it as the grid's texture — with the grid's extents set to the map's precise coverage, so glyphs and map features line up.

No account and no API key are needed. Three map styles are built in:

Style	Source	Good for
Streets (default)	OpenStreetMap	Cities, roads, place names
Satellite	Esri World Imagery	Terrain, land cover, aerial context
Terrain	OpenTopoMap	Elevation shading, contours, trails

The provider's required attribution is stamped into the image corner, so it stays with the scene wherever the file goes.

Using it

1. Load or build a scene whose points sit on a World Grid (children of a type-6 node, translate_x = longitude, translate_y = latitude).
2. Select the grid — press G, or pick it in the node table.
3. Click Fetch Basemap… in the World Grid panel.
4. The lon/lat window is prefilled from your data (with a little padding); the dialog previews exactly what a fetch will do — zoom level, tile count, output size — as you adjust it. Fit to Children restores the data-driven window after manual edits.
5. Click Fetch. The map appears under your data.

The image is written into the scene's media/ folder (as zz_basemap_grid<id>.png) beside the node CSV, so the basemap loads with the scene from then on — including through drag-and-drop and zip sharing. Saving the scene also persists the extents and texture assignment; other nodes' texture_ids are adjusted automatically if the new image changes the media numbering. Refetching for the same grid overwrites the same file in place.

Details worth knowing

• The map is reprojected. Tile servers publish Web Mercator; a World Grid drapes its texture linearly in latitude (plate carrée). GlyphViz resamples the imagery so the two agree — without this, points at US latitudes would sit tens of pixels off the map.
• Tiles are cached on disk (%LOCALAPPDATA%\GlyphViz\tile_cache), so refetching a region — or fine-tuning its window — costs little or no network traffic. Fetches are capped at 60 tiles, and the zoom level is chosen automatically to fit that budget at roughly screen resolution.
• Flat grids only. A regional map can't wrap a globe; switch the grid's Shape to Flat Rectangle first. (A globe still takes any whole-earth equirectangular image the ordinary way, via texture_id.)
• Aspect ratio: the fetched image has square pixels in degree space. For a locally true-to-shape map, set the grid's scale_y ≈ cos(mean latitude) × scale_x, as usual.
• Regions crossing the antimeridian (±180°) aren't supported yet.
• The fetch logic lives in glyphviz_core/basemap.py, separate from the Qt dialog, and is tested offline with a mocked tile server (tests/test_basemap.py).