3 ms·

Many people who haven't had the misfortune of working with geospatial data underestimate how unbelievably hard is to make a good map, let alone a global one.

ImaCake 3y ago
Is this because of the data quality and difficulties with merging across CRSes or otherwise slightly differently aligned datasets? I dabble in geospatial data for my work in air quality modelling, accuracy for me means being within approximately 10-50 meters. Even under those very loose constraints I find the data handed to me by clients is often not good enough. Incomplete AutoCad dxfs, PDFs, and dubious SHPs all make the work much harder than it needs to be.
- AlotOfReading 3y ago
  It's everything. The problem domain for Google maps is effectively "everything on Earth". I haven't worked with gmaps specifically and can't claim specific expertise there beyond some social conversations with people on the team, but some fun things I've encountered include: * Roads that have no physical delineations (e.g. an entire valley is the road). * Landscape features can change rapidly (e.g. forest fires rendering roads unusable on a minute-by-minute basis). * Landscape features can change slowly (e.g. erosion, continental drift) * Landscape features can change slowly and rapidly (e.g. features on glaciers). * Data that's flat out wrong for political reasons (e.g. disputed territories, GCJ-02, hidden "things"). * Data that's flat out wrong for technological reasons (e.g. GPS jamming). * Things that are named in languages without written forms. * Things that have official names other people consider offensive (e.g. Piestewa peak). When you make a map, all of these and more become your problem. Every edge case anywhere in the world is potentially something you have to worry about.
- cwmma 3y ago
  In addition to what the other commenter said, disparate sources with incompatible schema, often updated at a glacial pace are a big problem and possibly a root cause of the issue in the article.
strken 3y ago
It's quite fun trying to work out where an actual walking track is based on a printed topographic map (has good coverage of advertised official tracks but misses some), OSM (has nearly everything but tends to hallucinate non-existent tracks), the output of a local map-maker (compiles OSM and other sources but sometimes has the same track twice in slightly different places), and Google etc. (doesn't show anything a hatchback can't traverse, but has good satellite imagery that can show some tracks). This weekend I'm going to go explore one of the OSM tracks and see where it's a total hallucination, old and overgrown, or real.
- RicoElectrico 3y ago
  What do you mean by "hallucinate"? FYI most of the time it's a human drawing what they're seeing on the aerial imagery. I know many instances in which someone mapped a track through a field which subsequently got plowed by the field owner, but otherwise I have no idea. Could you tell any specifics?
  - mike_d 3y ago
    Imagine you draw a line following a trail on a map. Looks good, ship it! Now someone else loads that same line on their computer and it looks like a jagged mess because they are twice as zoomed in on the map as you were. Oops. What about the wide parts vs narrow parts of the trail? Do you represent that as two lines or just keep one down the middle? You send your trail to a friend who overlays it on their map that uses a different datum? How were the photos from the airplane assembled, and how did they represent a round object on a flat image? Did they have a good GPS lock when they took the photos, or did they even bother to check? What if the line you created is to be used 100 years in the future when the center of mass of the earth or magnetic north has shifted, how does your coordinate system account for that? I know just about enough GIS stuff to fit on a few index cards, but I quickly realized it is way more complex than how simple Google Maps makes it out to be.
  - strken 3y ago
    Sorry, hallucinate in the sense that the map says there's a track but there isn't anything there, whether or not it was drawn by a human. I meant it as an allusion to the map tripping balls but forgot that the overlap with AI terms would confuse HN. With OSM I think a lot of walking tracks are from GPS traces uploaded by volunteers, so maybe sometimes stuff sneaks in. Or maybe the map shows old tracks that have since been erased by rangers. Or maybe there's a nearby track that has been marked down in the wrong place.

ImaCake 3y ago

Is this because of the data quality and difficulties with merging across CRSes or otherwise slightly differently aligned datasets? I dabble in geospatial data for my work in air quality modelling, accuracy for me means being within approximately 10-50 meters. Even under those very loose constraints I find the data handed to me by clients is often not good enough. Incomplete AutoCad dxfs, PDFs, and dubious SHPs all make the work much harder than it needs to be.

AlotOfReading 3y ago
It's everything. The problem domain for Google maps is effectively "everything on Earth". I haven't worked with gmaps specifically and can't claim specific expertise there beyond some social conversations with people on the team, but some fun things I've encountered include: * Roads that have no physical delineations (e.g. an entire valley is the road). * Landscape features can change rapidly (e.g. forest fires rendering roads unusable on a minute-by-minute basis). * Landscape features can change slowly (e.g. erosion, continental drift) * Landscape features can change slowly and rapidly (e.g. features on glaciers). * Data that's flat out wrong for political reasons (e.g. disputed territories, GCJ-02, hidden "things"). * Data that's flat out wrong for technological reasons (e.g. GPS jamming). * Things that are named in languages without written forms. * Things that have official names other people consider offensive (e.g. Piestewa peak). When you make a map, all of these and more become your problem. Every edge case anywhere in the world is potentially something you have to worry about.
cwmma 3y ago
In addition to what the other commenter said, disparate sources with incompatible schema, often updated at a glacial pace are a big problem and possibly a root cause of the issue in the article.

strken 3y ago

It's quite fun trying to work out where an actual walking track is based on a printed topographic map (has good coverage of advertised official tracks but misses some), OSM (has nearly everything but tends to hallucinate non-existent tracks), the output of a local map-maker (compiles OSM and other sources but sometimes has the same track twice in slightly different places), and Google etc. (doesn't show anything a hatchback can't traverse, but has good satellite imagery that can show some tracks). This weekend I'm going to go explore one of the OSM tracks and see where it's a total hallucination, old and overgrown, or real.

RicoElectrico 3y ago
What do you mean by "hallucinate"? FYI most of the time it's a human drawing what they're seeing on the aerial imagery. I know many instances in which someone mapped a track through a field which subsequently got plowed by the field owner, but otherwise I have no idea. Could you tell any specifics?
- mike_d 3y ago
  Imagine you draw a line following a trail on a map. Looks good, ship it! Now someone else loads that same line on their computer and it looks like a jagged mess because they are twice as zoomed in on the map as you were. Oops. What about the wide parts vs narrow parts of the trail? Do you represent that as two lines or just keep one down the middle? You send your trail to a friend who overlays it on their map that uses a different datum? How were the photos from the airplane assembled, and how did they represent a round object on a flat image? Did they have a good GPS lock when they took the photos, or did they even bother to check? What if the line you created is to be used 100 years in the future when the center of mass of the earth or magnetic north has shifted, how does your coordinate system account for that? I know just about enough GIS stuff to fit on a few index cards, but I quickly realized it is way more complex than how simple Google Maps makes it out to be.
- strken 3y ago
  Sorry, hallucinate in the sense that the map says there's a track but there isn't anything there, whether or not it was drawn by a human. I meant it as an allusion to the map tripping balls but forgot that the overlap with AI terms would confuse HN. With OSM I think a lot of walking tracks are from GPS traces uploaded by volunteers, so maybe sometimes stuff sneaks in. Or maybe the map shows old tracks that have since been erased by rangers. Or maybe there's a nearby track that has been marked down in the wrong place.