Print a Map to Scale (PDF and PNG)

Why a scaled map print differs from a screenshot

If you print a screenshot of a web map, nobody knows how many metres one centimetre on paper represents; it depends on screen pixel density, zoom level and the printer's fit-to-page setting. With a scaled print the paper size and scale come first: at 1:1000 one centimetre on paper is exactly 10 m on the ground. This tool works out the print area for the paper and scale you choose, shows it as a frame on the map and renders the basemap at that scale as a PDF or PNG. It is useful for a field sketch, a location plan for a permit application or a satellite image for a project file.

How to use it

1. Choose the paper size (A4 to A0), orientation and scale. Use the custom scale for values not in the list.
2. Drag the red frame on the map, or pan the map and press "Centre the frame". If you know the coordinates, type the latitude and longitude.
3. Choose the basemap: satellite imagery, topographic map, a plain gray canvas or OpenStreetMap.
4. Fill in the title, subtitle, date, author and note. Add a coordinate grid if you need one, or load a GeoJSON, KML or KMZ layer such as a parcel boundary.
5. Press PDF or PNG. When printing, select 100% (actual size) in the printer dialog.

How the scale is kept

Web maps use the Web Mercator projection, in which scale changes with latitude: the further from the equator, the more the map enlarges the ground. At 40° latitude one Web Mercator metre is only about 0.77 m on the ground, and at 60° only 0.5 m. The tool calculates this enlargement at the middle latitude of the frame and removes it. The correction is made separately for the east-west and north-south directions on the WGS84 ellipsoid, so a 50 m scale bar on a 1:1000 print is exactly 5 cm on paper.

The tile level is chosen from the scale and the dpi. At 1:1000 and 300 dpi each output pixel covers about 8.5 cm on the ground. If the most detailed level of the basemap is coarser, tiles are enlarged and the tool shows a warning; the scale is still correct, the image is simply softer. For basemaps with labels (Topo, Gray, OSM) the level is chosen so that labels stay readable. Large sheets at high dpi need a lot of browser memory, so the output size is capped and the resolution is lowered automatically if needed.

Coordinate grid

The grid is drawn with an interval that gives about five lines across the print area, with values along the edges. For the UTM grid the zone is detected from the frame; the 3° TM grid picks the nearest central meridian and matches the Turkish ITRF96 system. On a Web Mercator basemap UTM and TM lines look slightly tilted because of meridian convergence; this is correct, as each line is computed through the projection.

Data and method

The basemaps are Esri World Imagery, World Topographic Map, Light Gray Canvas and OpenStreetMap tiles; their credits are read from the service and written on the bottom strip of the output. The OpenStreetMap tile usage policy does not allow bulk downloads, so the tile count for that basemap is kept low. The PDF is built with jsPDF 2.5.2 (MIT licence) and the Noto Sans font (SIL Open Font License), which covers Latin, Turkish and Cyrillic characters. Grid transformations use proj4js 2.9.0 (MIT), KML reading uses @tmcw/togeojson 5.8.0 (BSD-2-Clause) and KMZ files are opened with JSZip 3.10.1 (MIT). The map runs on Leaflet 1.9.4 (BSD-2-Clause).

Accuracy limits

• The scale is exact at the middle latitude of the frame. Because Web Mercator scale varies with latitude, very large areas (for example A0 at 1:100,000) show deviations of a few parts per thousand at the top and bottom edges.
• The satellite image itself may be offset by a few metres, so roads and buildings may not line up exactly with surveyed drawings.
• The output is not an official map, title plan or planning document. Printer margins and fit-to-page settings change the scale.

For organisations

If your team needs a web mapping application with its own scaled print templates, you can learn more on the Rodosto Teknoloji website or send us a message.