Lake Depth Maps Explained: Bathymetry for Laser Makers

Bathymetry is the measurement of depth under water. It is the topographic map of a lake bed. Survey crews take soundings (depth readings) across the lake, and those readings are turned into contour lines: a line where the bottom is 10 ft down, another at 20 ft, and so on.

A laser lake depth map uses those contours as cut lines. Each contour becomes the edge of a layer. Stack the layers and the lake bed steps down from the shoreline to the deepest point, so the shape of the bottom is something you can see from across the room.

Lake owners connect with their lake strongly. The shoreline reads instantly to anyone who has spent a summer on it, and the deep hole is the spot every angler already knows about. That is why lake maps are a deep gift niche, and why each lake is its own small market.

Depth is not part of ordinary street map data. OpenStreetMap has shorelines but not lake beds. Depth comes from surveys, and in the US those are published lake by lake, not as one national dataset.

• The Great Lakes. NOAA publishes bathymetry for the Great Lakes, including contour files for several of them.
• State agencies. Some state natural resource departments publish lake survey contours. Minnesota's DNR publishes bathymetric outlines and contours for its surveyed lakes as a free download.
• Paper and PDF charts. Many fishing charts exist only as images. Tracing them by hand is how a lot of early builds were made, and you should check the publisher's terms before selling pieces made from them.

Coverage is uneven. Some states publish no vector contours at all, and small private lakes are rarely surveyed. Plan for that before you promise a customer "any lake."

How MappSmith handles it

MappSmith uses real depth soundings from public lake surveys where they exist (Surveyed). For a lake with no published survey it shapes the bed from the shoreline (Simulated) and marks it Estimated, so you never pass a guess off as a survey. You can type the real deepest point in feet to rescale the whole bed, and choose a bed shape such as a gentle bowl, steep sides, or a ledge and drop. If a survey's contours don't close into cuttable shapes, the Studio switches to Simulated and tells you.

More bands means a smoother slope but a taller stack, more sheets and more glue-up. The right count depends on the lake, the size of the piece and your stock thickness.

• Space the thresholds by the lake, not by round numbers. A shallow lake with a deep hole needs more bands near the bottom. Use the lake's own surveyed levels.
• Stop short of the maximum. A band means "deeper than D." Set one at the very deepest point and it encloses nothing, so you cut an empty sheet.
• Drop tiny islands. Little holes and islands at depth burn away or fall out. Set a smallest-piece limit and lose them.

MappSmith's lake depth card builds 3, 5, 8 or 12 bands in one step, with thresholds taken from the lake's surveyed levels, and allows up to 16 water layers if you set them yourself. Each band stays its own editable layer.

This is where many first lake maps go wrong. People who have built a topographic map stack the contours the same way: each contour line becomes an island piece, glued on top of the last. On a mountain that is right. On a lake it is backwards. The deepest water ends up as the highest point, the shoreline sits lowest, and the lake looks like a hill.

Think of depth as negative height. The lake is a bowl, so each layer is a sheet with a hole in it, and the holes get smaller as you go down.

1. 01Backer (bottom)A solid sheet. It shows only through the deepest hole, so it gets the darkest color.
2. 02Deep bandA sheet with the area deeper than your deepest threshold cut out. Small hole.
3. 03Middle bandsEach one up, the hole grows to the next shallower contour.
4. 04Shallow bandThe hole is just inside the shoreline. The lightest blue.
5. 05Land (top)The whole lake cut out along the shoreline, with streets and the name on top.

Look down into the finished piece and it steps down from the shore to the deep spot, darker as it goes, just like the water. MappSmith builds the stack in this order: the deepest sheet sits lowest and acts as the backer, and your street map stays on top unchanged. Turn on glue guides and each layer gets a light line showing where the next one sits.

Depth reads best as a gradient. Shallow water is light blue, deep water is dark. You can get that three ways.

The top couple layers are Proofgrade Medium Maple Plywood, and the rest are Home Depot 1/4 inch plywood, b/c they are supposed to represent a bigger drop in depth (nothing to do with it being dirt cheap…)

A maker's Lake Murray bathymetric map, Glowforge owners forum

MappSmith's lake depth preset sets every band to blue acrylic in the 3D preview and shades them light to dark by rank, so you can show a customer the gradient before you cut. Preview colors only change the look on screen; your files are the same.

• Mask before cutting the light top layers to keep char off the shoreline edges.
• Use MDF for a painted water base. One maker warns that thin plywood tends to warp when painted on one side.
• Wipe, then prime, before paint. Laser residue wipes off with rubbing alcohol, and primer seals the wood so paint bonds.
• Glue sparingly. Brush glue on the back, away from the cut edges, and press under weight with wax paper. Clamps squeeze out more glue than you expect.
• Consider resin. One maker filled each lake cutout with resin, sanded it, and engraved the depth numbers, so they look like they float in the water.
• Label the depth. A max-depth line in the frame band turns a pretty map into a chart the owner will point at.

For more on stain, resin and glue-up, see premium map finishing. For the lake product itself, see lake depth maps.