Map sources

This map uses satellite imagery with numbered geographic features, municipal boundaries, and river and canal centerlines. Feature data was retrieved in September 2026.

Satellite imagery

Satellite tiles come from Esri World Imagery. Image dates and providers vary by location and zoom. Attribution: Esri, Vantor, Earthstar Geographics, and the GIS User Community. The images are not a live feed and require an internet connection. Imagery is streamed from its provider; it is not included in the downloadable geographic data below.

Geographic features

Geographic data is derived from OpenStreetMap contributors, licensed under the Open Database License (ODbL). Source geometries were retrieved through Nominatim: lake responses on September 3, 2026; municipal limits, connecting waters, and canals on September 8, 2026. Download the derived map data and feature coordinates (JavaScript containing JSON, ODbL).

Coordinates are WGS84, longitude then latitude. Leaflet displays the map in Web Mercator (EPSG:3857), north up, with a local metric scale. Topology-preserving simplification tolerances were 0.001° for lakes, 0.0005° for municipal boundaries and Lake St. Clair, and 0.00025° for river and canal centerlines. Polygon holes are preserved.

Municipal outlines show legal city limits, which can include water; they are not urban footprints. City anchors use city-center coordinates inside those boundaries. Connecting-water and canal anchors sit on their source centerlines. Numbers stay at their locations whenever there is room. Only crowded labels move; short pointers connect them to dots on the exact geographic anchors. These features are suitable for regional orientation, not surveying or navigation.

Fox River means the lower Wisconsin river entering Green Bay. The Chicago canal number sits near Lockport. The Welland Canal number follows the active canal near Port Colborne. The St. Lawrence Seaway number locates one river reference point east of Lake Ontario; it does not represent the whole seaway system. The St. Clair River is connecting geography without a separate question.

St. Lambert Lock: an approximate point locator near Montréal at 45.494° N, 73.5172° W, added September 16, 2026. Cross-checked against the Seaway authority’s lock reference (Table 8, NAD27) and Waterway Guide. Rounded regional teaching location, not a surveyed lock boundary or navigation coordinate. Mastery uses the same 25 km regional allowance as other places.

Route cross-checks: the Seaway authority’s Welland Canal map and locks and channels overview; the Library of Congress Chicago canal survey; and Michigan EGLE’s Detroit River overview.

Mastery: locating places without markers

Mastery checks your tap against water-area polygons, municipal boundaries, and mapped river/canal centerlines. The water footprints use OpenStreetMap shorelines and island holes, including Saginaw Bay. Georgian Bay also uses the official Natural Resources Canada / Canadian Geographical Names Database bay extent (FBHBM), intersected with Lake Huron water to exclude land.

Green Bay's open-water mouth follows the Door Peninsula and mouth island chain; its exact cut is an inferred gameplay boundary using NOAA's geographic account. The Straits of Mackinac use actual lake water within a local passage extent (45.62–46.08°N, 85.15–84.35°W). This is an inferred acceptance region, not an official surveyed feature boundary. Their coastlines come from the source water polygons.

Mastery accepts taps within 25 km of every feature, at any zoom level. Lake and city interiors count automatically; outside them, distance is measured to the nearest boundary. Rivers and canals use their mapped centerlines. This generous gameplay allowance also accepts nearby land or water. Lake questions use their whole water area, including named bays; bay questions use the bay footprint, with the same 25 km allowance. The Seaway question accepts the reference segment east of Lake Ontario shown by this game. These educational acceptance areas are not navigation or survey data.

Download the derived Mastery water footprints (JavaScript decoding to GeoJSON). Prepared September 10, 2026, in WGS84 longitude/latitude, with topology-preserving 0.001° simplification and retained holes. The derived dataset is © OpenStreetMap contributors, under ODbL 1.0, and contains information from NRCan/CGNDB licensed under the Open Government Licence – Canada. Source URLs and derivation methods are included in the download.

Software and type

Leaflet 1.9.4 handles the map, zoom, projection, and overlays. A copy of its BSD 2-Clause license is included. Outfit is bundled locally under the SIL Open Font License.

Scores and sound

Points reset each round. Your accumulated practice history and personal bests stay in your browser. Clear practice history under Map info → Your practice. High scores shows shared Classic and Mastery results side by side. If browser storage is unavailable, these records last only while the page stays open.

Time me connects to the game’s scoring service, which records the round’s answers, score and elapsed time. At the end of an unassisted full-map round, you may choose a nickname and post your result to the shared leaderboard. Posting is optional; nicknames, points and times are public once posted. Use a nickname that does not identify you. An anonymous browser cookie associates your posted best with this browser, so clearing cookies or using another device creates a separate identity. No account or email address is required. Reveal or a lost scoring connection makes the round ineligible for the shared board; you can still finish playing.

Unfinished rounds expire after two hours; completed round records expire after seven days. Posted bests remain until removed. Temporary hashed request identifiers help limit spam; raw IP addresses are not stored in the game database.

Sound effects are synthesized locally using Web Audio. Fireworks honor reduced-motion settings, and the finish chime honors mute. Opening this sources page leaves the round open in its original tab.

The link-preview artwork is an AI-assisted adaptation of NASA's August 28, 2010 Aqua/MODIS image of the Great Lakes, with added lettering and location rings. Original image credit: NASA / Jeff Schmaltz, MODIS Rapid Response Team, Goddard Space Flight Center. It is promotional artwork; the playable map uses the geographic sources described above.