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Author Topic: Linking Data from different maps across time  (Read 417 times)

sunnylew

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Linking Data from different maps across time
« on: 23 December 2016, 11:10:30 »
Something I've had trouble getting my head around is how to refer to representations of the same specific location over time.


Often you will find that a field in 1800 has become many more fields by 1900. You can also find that a few smaller fields have been combined and become a single larger field later on in time.


This can cause trouble when you want to say that such and such a field is the same as a field 100 years ago: it may very well not be - only parts of it are, though it still has the same name.


If all fields gradually became many smaller fields over time, we could use some sort of a descendency tree to link them together properly, but all manner of things can happen. I don't think a GEDCOM style of linkage could cope with fields that split, rejoin, then perhaps in the eastern corner combine with a different earlier field etc.


At the moment when I try to link different maps or properties over time I've taken to calling the specific area at that moment in time a "Parcel". I then link different parcels over time to a single "Location".


In my head, I see this as something like finding a record for Joe Bloggs and recording this as a "Name" fact for a "Person". There can be many names used over time, but it is still all the one person.


This approach works to a degree, but it's still very difficult to decide what the objective "Location" actually is.


Does anyone have any ideas on how to approach this?

PeterC

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Re: Linking Data from different maps across time
« Reply #1 on: 24 December 2016, 17:09:31 »
It is a significant issue, that I cannot pretend to have resolved. For me it applies to "dwellings" as much as fields, eg two families seem to be occupying two parts of a building in one census, but in another census it seems to be occupied by only one family. Maybe they are sharing, or maybe the dwelling is in two parts?

All I have done so far is to make sure that in my database all references to a particular dwelling (eg for a census record), are (almost) definitely to that (almost exact) dwelling. [The "almosts" come from recognising it is always a judgment call.] This does mean that I probably have quite a few duplicates, but I have a process for merging two "dwellings" into one when I am convinced they are the same one. I have done the same thing for people in my database where I am not sure they are the same person.

I envisage specifying the polygon shape of each dwelling if I know it, and using the mapping system to be able to see which ones are occupying the same geographical space. I have not done this so far, having limited it to a single point, but the potential is there.

I have toyed with the idea of data modelling the fields, whether into a tree structure or something else, but like you I think it could be too difficult. Fortunately people do not change their shapes as much as fields!

sunnylew

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Re: Linking Data from different maps across time
« Reply #2 on: 27 December 2016, 02:17:34 »

For the problem of individual dwellings, I had an idea that you could use Postcodes.


From memory you can download a dataset for the whole of the UK which can be mapped automatically in QGIS. Generally speaking, the land is becoming more subdivided when it comes to dwellings - though that of course isn't always the case - so you may find that most Postcodes link to houses from history.


I think being able to link via Postcode might also be a great way to get community engagement in your study: it makes it so easy for someone to see the history of their own home.

I've found the floor plans of dwellings to be tricky too - especially since the georeferencing process often distorts the shape of the building when it is adjusting to modern projection formats.


I was halfway through adding all of the buildings from the 1907 map of Hethersett when I realised that I just wouldn't be happy with their shapes. I'm now suffering from a bit of inertia - not wanting to face going back and redoing them all.


As my study is in Norfolk, I'm lucky that all of the 1946 Aerial Survey of England for Norfolk is online and already mapped to googlemaps. I plan to go back and overlay this on my map, tracing the buildings that still exist so that they look closer to how they should. This is daunting, as it means travelling 40 years in the wrong direction for my study :(


A trick I've found recently is to google recent online house auctions and sales for my village. If you've linked the postcodes Data then you can do a specific search for sales for the postcode that corresponds to a specific building and see what turns up. Otherwise, a general search will still give you many hits.


Many listings have a potted history of the building and all will have images - but more importantly: most have a floor plan with actual dimensions inside and out.


A lot of things will have changed in a hundred or so years, but comparison with the map should determine which parts were in existence way back when. You can even orient the modern floor plan as a raster over the building's footprint on your map to more clearly see the correct historic parts of the building.


I actually only thought of this last bit just now, and have to give it a try.


Otherwise, I've attempted to delineate fields by covering the whole village in points 5m apart from each other. The idea was that by using formulas in QGIS to list every point enclosed in a field, you could make a specific reference that could link to a series of specific places "on the ground". You could use this string to show when other fields over time correspond with some of the points, and that would signify shifts in area.


The drawback with this idea, I found, was that there's a question of just how accurately you've traced your map, and then confusion with subsequent maps that may be of the exact same area, but drawn slightly differently.

I still think this approach may work. To get around the above problem, I've done one very careful tracing of 1907. I plan to copy the field layer to a new layer for subsequent maps, and then join or split the copies based on the new map. That way the tracings should match perfectly if I work my way back in time sequentially through the maps.

It's all a bit overwhelming.

What I really look forward to doing is linking in historical records. This is just a framework!

I feel like a fisherman constantly cutting bait and never actually fishing.

PeterC

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Re: Linking Data from different maps across time
« Reply #3 on: 19 January 2017, 05:54:24 »
Would you like to let me try putting your study and the maps you have acquired/made into the prototype M4OPS system? It would be a useful opportunity for me to see how useful it could be in a real situation, and I would be happy to do it.

sunnylew

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Re: Linking Data from different maps across time
« Reply #4 on: 20 January 2017, 05:23:30 »
Hi Peter,


I'm very interested in attaching what I've done so far to your system.


I'd like to have a play with the system myself so that I can get a better understanding of the methodology. From what Ive seem, your system's far better than implementing in Google Maps because you can do more with it.


I still aim to make a 3D version of the town that can show the information I've gathered, but have realised that uploading to your system would be a good intermediary step. The data is still the data, and the representation is a different beast.


That being said, we have a 4 month old baby, and I have a lot less time for learning new things that I once did, so I may be calling on your for some help!


Cheers,


Lewis

PeterC

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Re: Linking Data from different maps across time
« Reply #5 on: 20 January 2017, 08:13:31 »
Hi Lewis

That's great. Please be aware that M4OPS is all very much a hand-cranked prototype at present - and it is mostly me that does the cranking for now. I am retired so have time and enjoy it, but my memory is just about good enough to remember my boys being that young - they now have four children between them! If this approach is useful for people then in time we should be able to make it easier for you to add maps.

There is a section of the forum for those responsible for an OPS, in which I am trying to add useful things. The place to start is for you to have a look at this post on Setting up your OPS on M4OPS (which I have just updated). Once you send me the name and location of your study I will set it up on M4OPS and we can take it from there.

It is probably best if we communicate the details about your study and set up off the forum now - either via the personal messaging or direct email (peter@pcooper.me.uk). But feel free to add comments and questions to the forum if you think they might be of more general interest.

Again can I emphasise that this is as much a learning experience for me as for you, because I want to develop my understanding of what we 'one-placers' want to achieve. I will be keen to continue to adapt M4OPS as we discover what we want to do.

I look forward to hearing from you

Peter

sunnylew

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Re: Linking Data from different maps across time
« Reply #6 on: 20 January 2017, 10:49:08 »
Cheers Peter.


I've already sent through a PM :)

PeterC

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Re: Linking Data from different maps across time
« Reply #7 on: 20 January 2017, 18:30:27 »
Hi Lewis

I have set up your One-Place Study in M4OPS, in a basic way. You can go directly to it using this link:  http://mapping4ops.org/ShowMaps/M4OPS-index.html?OPS=HTH . The main things you need to check first are summarised in the article on the forum I mentioned before, and things are easy for me to change.

Whenever you are ready to let me have a look at your data, or want to add any other maps do let me know. I look forward to seeing what we can do.


Peter
 

 

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