Hi Bin - just coming back to this.
actually I think the angular segmental graph is a really elegant representation.
The beauty is that this representation allows the graph to behave exactly like an axial map where segments line up exactly straight ahead (0 depth to each other), but when they change direction it quantifies the degree of that change between minor, right angle or even hairpin. It gives different results along the length of a line and these make real sense of variations we see in real cities along long straight streets. So its a more geometrically sensitive representation that happens also to ‘explain’ why the original axial representation worked and retains that property of axial continuity ‘collapsing’ distance. In this sense it behaves in a topological way like the axial map, but with added geometric sensitivity. My belief is that it will replicate many of the properties you have found for ‘named streets’ and the for continuity lines, but doing so without knowledge of the names, and without some of the potential pitfalls (e.g. M25 becoming a single node in the graph, or needing special case treatment etc.). Empirical data suggest that it performs better than or at least as well as axial (old style).
Now, on geometric sensitivity, the whole point of axial mapping is hat these are geometrically sensitive. Carlo Ratti gave a good example of this in what he thought of as a criticism of the axial line. In fact this isn’t a problem but a feature or axial representations is that in its construction the axial map is very sensitive to the geometry of the underlying map and captures aspects of that geometry in its topological formation. The fact that one can bypass the need to make and axial map and its rigorous geometric construction, using the somewhat less rigorous road centreline coupled to the angular segmental map is really just a pragmatic step. Particularly important if one is doing maps of very large areas - city regions and whole countries.
All the best,
Alan
> On 24 Feb 2016, at 16:41, Bin Jiang <[log in to unmask]> wrote:
>
> To supplement the previous message, the beauty or usefulness of London
> underground map lies exactly in its distorted geometry, simplified and
> distorted but becoming more informative topologically. In this
> connection, space syntax (old) goes a further step focusing on topology
> of individual routes or streets rather than geometric details. It is the
> geometric details that prevent us seeing the underlying scaling pattern
> of far more the less connected than the well connected.
>
> In this recent paper, we have provided further evidence on the power of
> this topological thinking, topological center, topological distance
> based on street blocks with London as one of the showing cases:
>
> https://www.researchgate.net/publication/287489085_Spatial_Distribution_of_City_Tweets_and_their_Densities
>
> BTW, a summer school on it:
> https://www.researchgate.net/publication/288832506_Summer_School_on_Topological_and_Scaling_Analyses_June_13-17_2016_Gavle_Sweden
>
> On 2016/2/24 14:39, Bin Jiang wrote:
>> Alan,
>>
>> Thanks for bring the discussion into another level!
>>
>> To honest, I have never been convinced by segment analysis which is
>> essentially geometric representation rather than topological
>> representation. By topological representation, I meant those
>> representations that enable us to see the underlying scaling of far more
>> the less connected than the well connected. Certainly, segment
>> representation is not the kind of topological representation. Relying on
>> angle analysis, the way you merge related segments into individual lines
>> with good continuity is essentially what we did in named streets
>> combined natural streets. The beauty of space syntax (old rather than
>> new ones) or the kind of topological representation I have been
>> promoting lies on its lack of geometric details but focusing topological
>> aspect only; see more discussions in this paper
>>
>> https://www.researchgate.net/publication/265911553_Different_Ways_of_Thinking_about_Street_Networks_and_Spatial_Analysis
>>
>>
>> This kind of topological representation can explain why Google works,
>> essentially there are far more less connected web pages than well
>> connected ones.
>>
>> https://www.researchgate.net/publication/2177752_Ranking_Space_for_Predicting_Human_Movement_in_an_Urban_Environment
>>
>>
>> In addition, to many other space syntax researchers, relying on space
>> syntax to predict individual travels is simply a fallacy. Space syntax
>> only tells collective behavior of crowds, which cannot be used to make
>> inference to any individual within the crowds. This is the same issue of
>> ecological fallacy; see more details in this paper:
>>
>> https://www.researchgate.net/publication/281936247_Can_Cognitive_Inferences_be_Made_from_Aggregate_Traffic_Flow_Data
>>
>>
>> I welcome comments and criticisms in particular.
>>
>> Cheers.
>>
>> Bin.
>> On 2016/2/24 13:28, Penn, Alan wrote:
>>> Bin,
>>>
>>> the way things here seem to have moved is towards measures of
>>> betweenness (choice) at a segment level, but using angular continuity
>>> between segments as the ‘cost’ has become the main set of measures
>>> (the other aspect is that of radius). Thus continuity is dealt with
>>> by angularity in the segment graph. If the A1 E4 is generally
>>> straight then that shows in the low cost of going straight ahead,
>>> however betweenness in general uses just segments of a longer
>>> alignment - e.g. some set of all to all angle minimising trips will
>>> come into Oxford St at Regent St and off at Berwick St - and so these
>>> trips are only assigned to the intervening segments. This means that
>>> the single axial line which runs the length of Oxford St and New
>>> Oxford St has different betweenness scores segment by segment all
>>> along its length. The M25 is a case in point - the single orbital
>>> motorway goes around London in a long pretty straight route
>>> (deviation from segment segment no more than few degrees each time)
>>> all with a single ‘name’, but it is the segments between junctions
>>> that gain different levels of traffic according to what they connect.
>>> This is where the angular segmental graph offers an elegant
>>> representation, and where amalgamating segments to single nodes in
>>> the graph according to either name or continuity would seem to me to
>>> be slightly odd.
>>>
>>> The same representation can also be used to generate angular depth
>>> measures for segments - closeness centrality - (analogous to measures
>>> of integration in the axial map).
>>>
>>> These dual measures (of closeness and betweenness) at different radii
>>> from the whole system (n) down to local pedestrian catchments (say
>>> 500m) give a useful set of combinations of measure that seem to
>>> capture many aspects of urban function and the way that different
>>> parts of streets play different roles at different scales.
>>>
>>> Thanks for the papers, I will read them.
>>>
>>> All the best,
>>>
>>> Alan
>>>
>>>
>>>> On 24 Feb 2016, at 09:13, Bin Jiang <[log in to unmask]> wrote:
>>>>
>>>> Alan, thanks for your comments!
>>>>
>>>> We merge central lines firstly according to their names and secondly
>>>> (if missing names) according to good continuity. Depending on your
>>>> data sources (e.g. openstreetmap), we have to chop the central lines
>>>> around all junctions before the merging processes. This is just a
>>>> technical issue. We do not eliminate little segments, but take all
>>>> segments. We generally use names in order to make the whole A1 Great
>>>> North Road into a single thing, which looks equivalent to E4 in
>>>> Sweden. A1 or E4 is indeed a single thing, which enables us to see
>>>> all streets in their wholeness rather than as parts or fragments
>>>> (more details in the following papers):
>>>>
>>>> https://www.researchgate.net/publication/272159333_Wholeness_as_a_Hierarchical_Graph_to_Capture_the_Nature_of_Space
>>>>
>>>> https://www.researchgate.net/publication/282272777_A_City_Is_a_Complex_Network
>>>>
>>>>
>>>> Cheers.
>>>>
>>>> Bin
>>>> On 2016/2/24 9:38, Penn, Alan wrote:
>>>>> Generally what you do is merge or otherwise eliminate little
>>>>> segments between intersections to give something close to a segment
>>>>> map. There are many problems as we know with road centre line data
>>>>> and the many very short segments around traffic islands etc. But
>>>>> they are pretty consistent in stopping and starting at
>>>>> intersections. You wouldn't generally use names because that would,
>>>>> for example, make the whole A1 Great North Road into a single
>>>>> thing. By using angular measures you can retrieve a lot of the
>>>>> properties of an axial representation - segments that continue
>>>>> straight ahead are zero weighted in depth, and so behave a bit like
>>>>> a single axial line in a graph. For very
>>>>> large maps this is the most practical approach.
>>>>>
>>>>> Alan
>>>>>
>>>>> Sent from my iPad
>>>>>
>>>>> On 24 Feb 2016, at 04:19, Bin Jiang <[log in to unmask]> wrote:
>>>>>
>>>>>> Alan, by centrelines, I suspect that they are merged centrelines
>>>>>> according to same street names and/or with good continuity, right?
>>>>>> If so, the centrelines are not individual street segments but
>>>>>> streets so to speak.
>>>>>>
>>>>>> Thanks and cheers.
>>>>>>
>>>>>> Bin
>>>>>> On 2016/2/23 22:08, Penn, Alan wrote:
>>>>>>> Or you could just use the centrelines. These are not quite so
>>>>>>> rigorously defined as axial lines but for most purposes will be
>>>>>>> adequate.
>>>>>>>
>>>>>>> Alan
>>>>>>>
>>>>>>> Sent from my iPhone
>>>>>>>
>>>>>>> On 23 Feb 2016, at 20:30, Aga Skorupka <[log in to unmask]>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> Hi Daniel (and Zeina).
>>>>>>>> Thank you so much for your reply!
>>>>>>>>
>>>>>>>> That is indeed correct - I did an offset from center lines of
>>>>>>>> streets and paths. That is the base map that I got.
>>>>>>>> BTW - (roads and streets’ ) center lines are available to
>>>>>>>> download for whole Norway here, for those of you who might be
>>>>>>>> interested in it.
>>>>>>>>
>>>>>>>> So I think I have two options: draw the axial lines myself (if
>>>>>>>> i get a better base map) or try Axwoman to generate them from
>>>>>>>> the center lines. Iim going to try to do both.
>>>>>>>>
>>>>>>>> Thanks again for your support with this!
>>>>>>>> It is so great to have an online community that is there to help!
>>>>>>>>
>>>>>>>> Best greetings,
>>>>>>>>
>>>>>>>>
>>>>>>>> Aga Skorupka
>>>>>>>>
>>>>>>>> +47 926 69 431 ◦ ◦ twitter ◦ linked in
>>>>>>>>
>>>>>>>> On Feb 22, 2016, at 9:53 AM, Daniel Koch
>>>>>>>> <[log in to unmask]> wrote:
>>>>>>>>
>>>>>>>>> Dear Aga,
>>>>>>>>>
>>>>>>>>> after a brief look at your dxf it seems you have extracted
>>>>>>>>> the outlines of paths and streets, is this correct? If this was
>>>>>>>>> pre-existing this may make sense, otherwise I would advocate
>>>>>>>>> drawing the axial lines manually, as this also allows you to
>>>>>>>>> take for instance elevation changes into account (I suspect
>>>>>>>>> there are such in Norway but I suppose it’s not so everywhere).
>>>>>>>>> Depending on the morphology you work in, first extracting paths
>>>>>>>>> and then drawing axial lines on them is not self-evidently the
>>>>>>>>> best procedure.
>>>>>>>>>
>>>>>>>>> However, I believe the automatically generated maps in Depthmap
>>>>>>>>> is better suited for situations where you rather have blocks as
>>>>>>>>> defining elements to generate from rather than narrow paths.
>>>>>>>>> AFAIK the reason for this is related to the theory behind axial
>>>>>>>>> maps.
>>>>>>>>>
>>>>>>>>> Looking at the size of the town, I think it is within the size
>>>>>>>>> where I would advocate making the axial map manually, taking
>>>>>>>>> better into account the full material morphology and not just
>>>>>>>>> street outlines. The alternative to that would to me be to use
>>>>>>>>> road-centre lines to generate a segment map, but for the size
>>>>>>>>> of town you work with manual seems the best.
>>>>>>>>>
>>>>>>>>> Importantly, if you wish to work with axial maps the conceptual
>>>>>>>>> ground needs to be clear; the exact location of a line matters
>>>>>>>>> only so far as deviations misrepresents the material
>>>>>>>>> morphology, and the method you chose to proceed is tied to the
>>>>>>>>> question which you are seeking to answer.
>>>>>>>>>
>>>>>>>>> Best
>>>>>>>>> Daniel
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> ____________
>>>>>>>>> Daniel Koch
>>>>>>>>> KTH School of Architecture
>>>>>>>>> [log in to unmask]
>>>>>>>>> www.arch.kth.se | www.kth.se/profile/dkoch/
>>>>>>>>> +46 8 790 60 25
>>>>>>>>>
>>>>>>>>> Editor, Journal of Space Syntax
>>>>>>>>> joss.bartlett.ucl.ac.uk
>>>>>>>>>
>>>>>>>>> Architecture in the Making
>>>>>>>>> Vice Director
>>>>>>>>> www.architectureinthemaking.se
>>>>>>>>>
>>>>>>>>> Architectural Morphology
>>>>>>>>> www.archmorphstockholm.se
>>>>>>>>>
>>>>>>>>> 7th International Space Syntax Symposium
>>>>>>>>> www.sss7.org
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> On 21 Feb 2016, at 09:00, Aga Skorupka <[log in to unmask]>
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>> Hi all,
>>>>>>>>>>
>>>>>>>>>> I am trying to run axial analysis on a dxf map of a small town
>>>>>>>>>> in Norway.
>>>>>>>>>> The file represents all walkable paths
>>>>>>>>>>
>>>>>>>>>> https://www.dropbox.com/s/a3mtzdg83j25zaa/aga.dxf?dl=0
>>>>>>>>>>
>>>>>>>>>> When I get depth map to draw axial lines it doesn’t ‘fit them
>>>>>>>>>> in’ the lines in some of the paths.
>>>>>>>>>> Is there some way around it? Can for example the axial lines
>>>>>>>>>> be made thinner to fit in in the paths?
>>>>>>>>>> Should I try to make the paths even wider (as of now they are
>>>>>>>>>> 4 m wide, and I would be risking that they would start
>>>>>>>>>> overlapping)
>>>>>>>>>>
>>>>>>>>>> I would greatly appreciate any thoughts and suggestions!
>>>>>>>>>> Thank you in advance!
>>>>>>>>>>
>>>>>>>>>> Best,
>>>>>>>>>> Aga Skorupka
>>>>>>>>>>
>>>>>>>>>> PS. My apologies if this is an issue that has been raised
>>>>>>>>>> earlier on this listserv!
>>>>>>>>>>
>>>>>> --
>>>>>> --------------------------------------------------------
>>>>>> Bin Jiang
>>>>>> Division of GIScience
>>>>>> Faculty of Engineering and Sustainable Development
>>>>>> University of Gävle, SE-801 76 Gävle, Sweden
>>>>>> Phone: +46-26-64 8901 Fax: +46-26-64 8758
>>>>>> Email:
>>>>>> [log in to unmask] Web: http://fromto.hig.se/~bjg/
>>>>>>
>>>>>> --------------------------------------------------------
>>>>>> Academic Editor: PLOS ONE
>>>>>> Associate Editor: Cartographica
>>>>>>
>>>>>> BinsArXiv:
>>>>>> http://arxiv.org/a/jiang_b_1
>>>>>>
>>>>>> Axwoman:
>>>>>> http://fromto.hig.se/~bjg/axwoman/
>>>>>>
>>>>>> ICA:
>>>>>> https://sites.google.com/site/commissionofica/
>>>>>>
>>>>>> Geomatics:
>>>>>> http://fromto.hig.se/~bjg/geomaticsprogram/
>>>>>>
>>>>>> RG:
>>>>>> https://www.researchgate.net/profile/Bin_Jiang3
>>>>>>
>>>>>> Högskolan i Gävle, 801 76 Gävle • 026 64 85 00 • www.hig.se
>>>>>>
>>>>>> För en hållbar livsmiljö för människan
>>>>>>
>>>>>> University of Gävle, SE-801 76 Gävle, Sweden • +46 (0) 26 64 85 00
>>>>>> • www.hig.se
>>>>>>
>>>> --
>>>> --------------------------------------------------------
>>>> Bin Jiang
>>>> Division of GIScience
>>>> Faculty of Engineering and Sustainable Development
>>>> University of Gävle, SE-801 76 Gävle, Sweden
>>>> Phone: +46-26-64 8901 Fax: +46-26-64 8758
>>>> Email:
>>>> [log in to unmask] Web: http://fromto.hig.se/~bjg/
>>>>
>>>> --------------------------------------------------------
>>>> Academic Editor: PLOS ONE
>>>> Associate Editor: Cartographica
>>>>
>>>> BinsArXiv:
>>>> http://arxiv.org/a/jiang_b_1
>>>>
>>>> Axwoman:
>>>> http://fromto.hig.se/~bjg/axwoman/
>>>>
>>>> ICA:
>>>> https://sites.google.com/site/commissionofica/
>>>>
>>>> Geomatics:
>>>> http://fromto.hig.se/~bjg/geomaticsprogram/
>>>>
>>>> RG:
>>>> https://www.researchgate.net/profile/Bin_Jiang3
>>>>
>>>> Högskolan i Gävle, 801 76 Gävle • 026 64 85 00 • www.hig.se
>>>>
>>>> För en hållbar livsmiljö för människan
>>>>
>>>> University of Gävle, SE-801 76 Gävle, Sweden • +46 (0) 26 64 85 00 •
>>>> www.hig.se
>>>>
>>
>> --
>> --------------------------------------------------------
>> Bin Jiang
>> Division of GIScience
>> Faculty of Engineering and Sustainable Development
>> University of Gävle, SE-801 76 Gävle, Sweden
>> Phone: +46-26-64 8901 Fax: +46-26-64 8758
>> Email: [log in to unmask] Web: http://fromto.hig.se/~bjg/
>> --------------------------------------------------------
>> Academic Editor: PLOS ONE
>> Associate Editor: Cartographica
>>
>> BinsArXiv: http://arxiv.org/a/jiang_b_1
>> Axwoman: http://fromto.hig.se/~bjg/axwoman/
>> ICA: https://sites.google.com/site/commissionofica/
>> Geomatics: http://fromto.hig.se/~bjg/geomaticsprogram/
>> RG: https://www.researchgate.net/profile/Bin_Jiang3
>>
>>
>> [Högskolan i Gävle]
>>
>> Högskolan i Gävle, 801 76 Gävle • 026 64 85 00 •
>> www.hig.se<http://www.hig.se>
>>
>> För en hållbar livsmiljö för människan
>>
>> University of Gävle, SE-801 76 Gävle, Sweden • +46 (0) 26 64 85 00 •
>> www.hig.se<http://www.hig.se>
>
> --
> --------------------------------------------------------
> Bin Jiang
> Division of GIScience
> Faculty of Engineering and Sustainable Development
> University of Gävle, SE-801 76 Gävle, Sweden
> Phone: +46-26-64 8901 Fax: +46-26-64 8758
> Email: [log in to unmask] Web: http://fromto.hig.se/~bjg/
> --------------------------------------------------------
> Academic Editor: PLOS ONE
> Associate Editor: Cartographica
>
> BinsArXiv: http://arxiv.org/a/jiang_b_1
> Axwoman: http://fromto.hig.se/~bjg/axwoman/
> ICA: https://sites.google.com/site/commissionofica/
> Geomatics: http://fromto.hig.se/~bjg/geomaticsprogram/
> RG: https://www.researchgate.net/profile/Bin_Jiang3
>
> [Högskolan i Gävle]
>
> Högskolan i Gävle, 801 76 Gävle • 026 64 85 00 • www.hig.se<http://www.hig.se>
>
> För en hållbar livsmiljö för människan
>
> University of Gävle, SE-801 76 Gävle, Sweden • +46 (0) 26 64 85 00 • www.hig.se<http://www.hig.se>
|
