Why the Map May Look Different from the Unit

Use this when

The GPS track in HumVision looks different from the track shown on your Humminbird unit, or you notice the path does not align exactly with waterways on the basemap.

Why the track may look different

The map source is different

Your Humminbird unit uses its own built-in chart data (Navionics, LakeMaster, AutoChart, or similar). HumVision draws the same GPS coordinates on a separate basemap. The basemap is OpenStreetMap, MapTiler, Esri satellite, or whichever style you have selected in Settings. Those basemaps are updated on different schedules and rendered differently, so the visual context around the track may not match what you saw on the unit.

Outlier coordinates are filtered out

Humminbird units occasionally write a small number of clearly wrong GPS positions — coordinates that are far outside the expected area of the recording. HumVision removes the top and bottom 1% of positions by latitude and longitude before drawing the track. This prevents a single bad point from zooming the map out to show a line stretching across a continent. Those same outlier points are still present in exported GPX and KML files, which use raw coordinates.

The unit may smooth or project its displayed track

Humminbird units apply their own display-side smoothing and interpolation to the chart track. HumVision draws coordinates exactly as stored in the sonar file with no additional smoothing. The raw track may show more visible jaggedness at low speeds or when the boat was stationary.

The GPS receiver has inherent accuracy limits

Consumer GNSS receivers typically have a positional accuracy of 2 to 5 meters under open sky. In narrow channels, near tall banks, or under canopy, accuracy can degrade further. Both the unit's display and HumVision reflect this.

What is normal

• The track follows the correct waterway but has slight drift — normal GNSS accuracy variation.
• The track looks jaggy near turnaround points or slow drifts — the unit was moving slowly, so individual GPS samples are spaced close together and noise is more visible.
• Short gaps in the line — the unit temporarily lost satellite lock, so those pings were filtered out.
• The track looks compressed or slightly offset compared to the unit screen — different basemap projections and rendering. The coordinates are the same.

When to be concerned

• The track appears in a completely different body of water or wrong country. This usually means the unit had no GPS lock and wrote 0,0 coordinates that partially passed the filter, or there was a firmware-level GPS error. Try re-loading the recording; if the problem persists, the source coordinates may be corrupt.
• The track doubles back on itself in ways that do not match the actual route. A small number of flipped or transposed coordinates can occur on some older firmware. Export the GPX and inspect the raw coordinates.
• The entire track is offset by the same distance in one direction. This is uncommon with modern GNSS, but if it happens consistently across multiple recordings from the same unit, the unit may have a datum or calibration issue.

If you are unsure whether the data is usable, export the track as GPX or KML and compare it against a known reference in Google Earth or your GIS tool of choice.