Blake Island treasure mapping. Yar!

Posted by cjpapetti on 20 February 2021 in English (English).

Hi from Blake Island Above image: Exploring the island with my partner.

My favorite camping spot near Seattle is Blake Island State park because I can literally walk from my apartment to the ferry which drops me off at the campground without any need for a car!

The Blake Island trails are not fully mapped on Open Street Map so I guess that’s my job now? Here we go!

Obligatory before and after shots: Before After

Step 1: Find and import good data sources

The more data I have for JOSM (Java Open Street Map Editor) the more accurately I can trace the trails:


  • Open Street Map data: Downloaded the base data for this region from OSM as usual.
  • Bing aerial satellite imagery: Enabled in the image menu
  • Strava heatmap: This layer ended up having no data for * Blake Island because the heatmap only shows running and biking routes not hiking.
  • Washington State Park trail database Link: Learned how to import a shape file to JOSM. It requires the OpenData plugin which was installed from the plugins menu in JOSM. This imported the trail shapes for the entire state, which took a few minutes. I need to learn how to import a specific portion of a shape file to be more efficient in the future.
  • Open Street Map GPS traces: Enabled in the image menu.
  • Wooden painted map from signpost at park: I had a photo of this map which had some nice extra details about trail names that I couldn’t find online.

Step 2: Integrating new trail data onto existing map

  1. Select existing trails on OSM layer: There are a few existing inaccurate trails that need to be removed so they don’t overlap my new trails. Using the search function I selected only the “highway” tags within a specific layer. Note: it’s very important to use the “find in selection” search option so you don’t accidentally select and delete all highway paths on the whole city map!
  2. Remove existing trails from OSM layer: Now that the trails are selected, delete them from the OSM layer so they don’t overlap my new, more accurate trails. More on the ethics of this later.
  3. Copy and paste trails for State Park layer to OSM layer: Ctrl+Alt+V pastes things into the same position as their original layer. For some reason the regular Ctrl+V shifts the location when you paste which is pretty useless.
  4. Modify tags on new trails: The trail tags need to match the OSM standards found here link. The state park trails were imported with a lot of existing tags. Some of these are useful and will be renamed to match the OSM standards. For example the TR_NM tag will be renamed as “name”. Other tags will be removed. Some new tags will also be added to match OSM standards. Before and after images of tag/field cleanup: original source tags modified tags

Step 3: Nodes and ways cleanup

oh nodes! I ran the validator tool to identify any errors. Apparently the imported Washington State trail shape file has many broken junctions among other things. Time for some tedious manual node adjustments. I cleaned up around 50 broken junctions. I wonder if there is a script or function to do this automatically within a certain margin of error? It would’ve saved me about 30 minutes.

Step 4: Map source dissonance. Who’s telling the truth?

4 reference maps plus my memory from own visit to the island tell me 5 different stories about the trail locations and names. Which one is most accurate? I had to combine details from each map to create the most accurate representation.

  • Washington State trail data: I used this map for the most precise geolocations of the trails.
  • Official State Park illustrated PDF map: I used this map for the trail names.
  • Wooden map painting from park signpost: This had extra details about trail names.
  • OSM heatmap: I used this to help me verify if some of the mapped yet unnamed trails were in-fact real trails. Washington state data Illustrated pdf map Wooden painted sign OSM GPS traces
Location: Kitsap County, Washington, United States

Comment from MapMakinMeyers on 22 February 2021 at 02:57

I love this post! Thanks for sharing!!!

Comment from spacereno on 23 February 2021 at 05:16

Nice!! 😍

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