Charts and Base Maps

The Built-in Base Map

qtVlm ships with a high-resolution worldwide base map that downloads automatically during installation. This base map shows coastlines, major features, depth shading, and geographic labels — enough to orient yourself and plan routes without any additional chart purchases. For weather routing purposes, the base map is often sufficient since you're primarily working with GRIB data overlaid on ocean areas.

The base map uses a tile-based system similar to Google Maps or OpenStreetMap. As you zoom in, more detail appears: coastal features, harbor outlines, small islands. At high zoom levels near shore, you'll see the limits of the base map — it's not a navigational chart and shouldn't be used for pilotage. But for route planning at the scale where weather routing operates (tens to hundreds of miles), it provides excellent geographic context.

You can adjust the base map's appearance under Options → Display. Key settings include night mode (which dims the map for easier reading in low light), land color, and sea color. Some sailors prefer a muted base map so the GRIB overlay stands out more clearly; others want maximum geographic detail. Experiment to find what works for your eyes.

Raster Charts (BSB/KAP and GeoTIFF)

Raster charts are digital images of traditional paper charts — scanned and georeferenced so they display at the correct position on your screen. The most common format for US waters is BSB/KAP, which is the format NOAA uses for its free raster navigational charts (RNCs). These are full navigational charts with depth soundings, aids to navigation, hazards, and all the detail you'd find on a paper chart.

To load a raster chart in qtVlm, go to Charts → Open Chart and select your .kap file. The chart appears overlaid on the base map at its correct geographic position. You can load multiple raster charts and qtVlm tiles them together, switching between charts as you zoom and pan. The transparency slider (Charts menu) lets you see the GRIB data through the chart or the chart through the GRIB — useful when you want weather data and navigational detail simultaneously.

GeoTIFF is another raster format — a standard image file (TIFF) with embedded geographic coordinates. Some chart services and custom charts are distributed as GeoTIFF. qtVlm handles these the same way as BSB/KAP files.

The main limitation of raster charts is that they're fixed-scale — a chart designed for 1:80,000 becomes pixelated if you zoom in much further and loses detail if you zoom out. For weather routing, this is rarely a problem since you're typically zoomed out to passage-planning scale.

Vector Charts (S57, S63, CM93)

Vector charts store chart data as objects — depth contours, buoys, land areas, shipping lanes — rather than as a fixed image. This means they scale cleanly at any zoom level, and individual objects can be queried (click a buoy to see its characteristics). They're the modern standard for electronic navigation and provide a superior experience to raster charts in most situations.

qtVlm supports several vector chart formats. S57 (.000 files) is the international standard for Electronic Navigational Charts (ENCs). NOAA distributes free S57 ENCs for US waters. S63 is the encrypted version of S57, used by hydrographic offices that charge for their charts — you'll need a license and permit to use these. CM93 is an older worldwide vector chart set from C-MAP that's widely available (often bundled with chart plotters) — qtVlm can read CM93 charts directly.

To load vector charts, go to Charts → Open Chart or configure a chart directory under Charts → Manage Charts. When you point qtVlm at a folder of S57 ENCs, it indexes them automatically and displays the appropriate chart as you pan and zoom — a seamless, quilt-like experience. The chart detail adjusts to your zoom level, showing only relevant information at each scale.

For weather routing, vector charts are particularly useful near departure and arrival points where you want to verify that your route doesn't cross shallow areas, traffic separation schemes, or restricted zones. The ability to query individual objects — clicking on a TSS boundary to confirm its limits — adds a level of precision that raster charts can't match.

MBTiles, Online Charts, and Chart Management

MBTiles is a tile-based chart format that packages raster or vector tiles into a single SQLite database file. It's compact, fast to render, and increasingly popular for offline chart storage. qtVlm supports MBTiles natively — load them through Charts → Open Chart. Some users create custom MBTiles from OpenSeaMap or other open-source chart data for areas where commercial charts aren't available or affordable.

qtVlm can also display online chart tiles when you have an internet connection. Under Charts → Online Charts, you can enable tile servers including OpenStreetMap, OpenSeaMap, and satellite imagery. These overlay on the base map and provide additional detail without downloading chart files. The obvious limitation is that they require internet — not available offshore.

The VisitMyHarbour chartsets deserve special mention. These are community-sourced harbor approach charts, anchorage details, and coastal cruising guides available through qtVlm. They're particularly strong in European waters and supplement official charts with practical cruising information.

Chart management in qtVlm is handled through Charts → Manage Charts, where you can configure chart directories, set loading priorities, and control which chart types display at which zoom levels. A typical setup might prioritize vector ENCs when available, fall back to raster charts for areas without ENC coverage, and always show the base map underneath everything.