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Advanced JOSM Work on Schools

Posted by alexkemp on 21 April 2020 in English.

Was it only yesterday that I finished NG school updates, then started working through schools within SG postcodes? For some reason I hit a couple of complex multi-site schools straight away, each of which gave mighty problems. The most recent was the fabulous Heath Mount School (incongruously the relation looks like a fish swimming to the left). My grandkids were due to attend that school until parental divorce intervened.

I find that documenting stuff helps to cement the lessons learnt, as well as giving me something to refer to if I forget, and hopefully will help other novices as well. So, here are some small techniques to use with JOSM to help get the job done, drawn from very recent experience.

School Layout: Look for an Architect PDF

Heath Mount School:

Heath Mount School

The latest school (link above) had an interactive map. I was in ecstasy! Most schools do not bother to mention the layout of their sites, let alone name the buildings, and not a single one of the thousand schools that I’ve mapped this last month had a website that bothered to include a map. Until this one. Quiver!

If building work has been carried out, then refer to the local council. They always publish documents that include a building layout. If all else fails then find the name of the architect involved & search their site.

Place all School Tags Upon the Cadastre

(see the previous Diary for more on this)

Almost all items within the interactive map had already been placed into OSM, but the tagging was minimal. Many were missing from Bing imagery, but present within Esri. No Cadastre was within OSM yet, but essentially the interactive map gave boundaries to the Cadastre and allowed me to establish it. A Relation was used to group all school facilities together.

This was the process:-

  1. Draw (if missing) & name all buildings
  2. Draw all areas & name them
  3. Create a Relation (name=Heath Mount School) with the main building as “outer” role
  4. Transfer all non-building tags from the building to the Relation
    (in this case all relation Members have the same address, so address/contacts are added only to the Relation)
  5. Add the other 6 Members to the Relation

These are the Relation Members:

  1. Heath Mount Lower School Year 3&4 (building)
  2. Heath Mount Nursery & Pre-Prep (building)
  3. Heath Mount Performing Arts Centre (building)
  4. Heath Mount Prep School Year 5-8 (building: listed_status=Grade I)
  5. Heath Mount Sports Grounds (a closed way: landuse=recreation_ground)
  6. Heath Mount Sports Hall (building)
  7. Heath Mount Stumble Trip Woods (a closed way: natural=wood)

Everything looked hunky-dory until I hit the Upload button. It produced both Errors & Warnings (always fix errors and try to fix warnings). Here are a series of both to avoid, and how to do so:

Do Not Add a Complex Multi-Polygon Building to a Relation

This was mentioned in the previous Diary..

A Multi-Polygon Building is a building with holes in the middle. As long as the building does not have holes it can be added to a Relation, else not (hint: a Cadastre around any building can be added).

Do Not Merge Two Adjacent Areas if Both are Within a Relation

The Sports Ground is adjacent to Stumble Trip Woods. Or at least, it was merged along a common line in the middle, but that gave a warning message which took hours to resolve:

Mixed type duplicated nodes

If you examine the (non-) join between these two areas at ultra-resolution, you will discover a distinct separation between them. Here is how to do that:

• Click on one of the nodes
• Press ‘3’ (zoom to selection)
• Press ‘+’ repeatedly until at max zoom

To see the point:

• Press with Middle-mouse-button on bottom line
• Press the Ctrl button to retain dialog on screen

The bottom edge is actually 2 x merged-areas (Woodhall Park + Heath Mount Sports Grounds). There is zero problem because only the Sports Grounds are in a Relation. However, the top edge is Stumble Trip Woods, and it is within the same relation. Hence the gap, which negates the warning.

To travel to a member of a Relation:

• Click the Edit button within the Relation window (Alt + Shift + R)
• Right-click on the Relation member
• Choose “Zoom to”
• Click Cancel
(the Member is now selected within the window)

The above also works with Warning & Error messages.

Set Buildings Inside an Area as ‘inner’

The Lower School Year, Nursery & Pre-Prep and Performing Arts Centre are all inner Members. That is because they sit within the Sports Grounds and gave an error when I set them as outer:

Role verification problem - Role for ‘‎Heath Mount Lower School Year 3&4‎ (8 nodes)’ should be ‘inner’ (1)

Do not Allow Same-Type Areas to Cross

This warning pre-dated my actions. I had copied Stumble Trip Woods around part of the existing natural=wood area. Unfortunately a small triangle of that wood crossed a square of wood to the north and that threw up a warning. A tiny rearrangement fixed the warning.

Phew. Hopefully that helps.


Comment from kucai on 21 April 2020 at 05:25

Always wondered: wouldn’t everything inside the school grounds boundary (amenity school polygon with barrier = fence maybe) be associated with the school without using a relation?

Been mapping for years, and other than river islands relations, I’ve stayed away from them. Too finicky.

Comment from alexkemp on 21 April 2020 at 06:01

Hi kucai.

Yeah, one of the very first things that I noticed within OSM was the antipathy of current mappers towards Relations. I was a database programmer, so it was different at my end. For users it makes little difference other than offering more links & inter-links to search with. And that, really, is the point, because without that Relation no inter-links become available.

Comment from alexkemp on 21 April 2020 at 06:30

Aha! Just met the perfect situation that can only be solved with a Relation:

Ivel Valley School has 2 sites on either side of Biggleswade:

At the moment they are mapped independently in OSM, and it is difficult for anyone to get to the other campus, or even know that it exists. I’m about to move each campus into a Relation and presto! They will be related & feature within each other’s links.

Comment from Polyglot on 3 May 2020 at 14:20

It seems like you are using multipolygon relations. What about site relations?


Comment from alexkemp on 3 May 2020 at 14:55

The wiki on Site Relations says ‘use multi for schools’ (see one of the other recent diaries - I forget which one - for proper quote & url). That seems conclusive to me.

Site seems to have all the disadvantages & none of the advantages of Multi. So, what about them?

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