Following Transects while BioBase Mapping

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A frequently asked question of BioBase users is how do you ensure proper coverage of a water body you want to map? Some years ago we published a blog on the topic of aquatic mapping strategies and transect design that is still very relevant today. Here we focus our attention on some practical tips and tricks that takes theory into practice and gives you guides or lines to follow on your Lowrance Chart. Note that we won’t walk you through every screenshot or setting, but rather point you to the key tools and features that will get you started. We do publish more in depth tutorials on This isn’t an exhaustive list, so please share additional tips and tricks in the comments!

For the planner: Design transects in GIS and import trail as .gpx into your Lowrance

ESRI Arc Solution

Figure 1. In the ArcTool Box, under Data Management Tools – Sampling use the Fishnet feature to create transects. Ensure the map is projected into some sort of meter projection (e.g., UTM).
Figure 2. Delete vertical lines and rotate feature to align transects perpendicular to the longest shoreline.
Figure 3. Merge lines prior to gpx creation so your Lowrance reads the .gpx as one trail rather than many. ArcPro has a feature that will convert .shp into .gpx so you can import into Lowrance

Free QGIS Solution

Figure 4: In the processing toolbox in QGIS search “grid.” Ensure the map is projected into meters (e.g., UTM or Mercator).
Figure 5. Create grid with overly large vertical transects that are easy to select and delete so all you are left with are the appropriate spaced horizontal transects. Make the grid overly large so you can rotate it and the grid stays within the lake.
Figure 6. Delete vertical lines, rotate 30 degrees and clip with the lake boundary polygon.
Figure 7. Merge lines in the Advanced Editing Toolbar, Remove the Meter projection, export layer as .gpx and import into Lowrance.

Create a .kml path in Google Earth and convert to .gpx

Shifting on the Fly: Use Course/Heading Lines and Range Rings

Figure 8. Configure your Lowrance Chart to display Course, Heading, and Range Rings.
Figure 9. Use Range Rings and scale bar on your Lowrance to judge how far apart your back and forth passes are from each other

Shifting on the Fly: Repurpose “Search and Rescue” Feature.

Create Transects on the fly with the Search and Rescue feature on any Lowrance HDS Gen 3 or newer, Elite Ti2 or Elite FS.

Do the same thing with Simrad NSS Evo. Up your game and get an autopilot to drive crisp transects

Shifting on the Fly: Concentric Circle

Figure 10. If you are mapping a small pond, try a concentric circle approach. Turn on a Trail on your Lowrance, start tracing the shoreline and slowly work your way into the middle, taking care not to cross over previously traveled tracks. This approach is about as easy as it gets to execute and you’ll get comprehensive coverage.

Author: biobasemaps

BioBase is a cloud platform for the automated mapping of aquatic habitats (lakes, rivers, ponds, coasts). Standard algorithms process sonar datafiles (EcoSound) and high resolution satellite imagery (EcoSat). Depth and vegetation maps and data reports are rapidly created and stored in a private cloud account for analysis, and sharing. This blog highlights a range of internal and external research, frequently asked questions, feature descriptions and highlights, tips and tricks, and photo galleries.

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