Milton | Network Analysis | Analysis

Milton Booklet No.5

Stage

Package

Analysis

Network Analysis of Streets

Prepared by Poppea Daniel, Marc Miller, Lwin Mar Kyaw, Xun Hern Liaw Urban Design Studies Unit, University of Strathclyde, Glasgow, September - October 2016

Network Analysis of Street

Content 3 Introduction Aims Methodology Technical notes

8 Part I Existing Network Betweenness Centrality Closeness Centrality Straightness Centrality

30 Part II Scenarios Scenario 1 Scenario 2 Scenario 3

41 Conclusions

Introduction

Aims

Look at Milton on a map of Glasgow and you might notice its relative isolation. Like many developments on the urban periphery, it suffers from a lack of connectivity to the rest of the city.

We have two key aims.

Walking around Milton, you might find the place confusing and illegible, and struggle to find something you could call its ‘core’.

Connectivity, inside Milton and to other parts of the city, is key. It allows places to be naturally central.

The first step is to map Milton’s current street network, and to analyse and interpret the current potential of streets in Milton to be more or less central.

The second step is develop and test several crude ideas for how you could alter the street network in and around Milton in order to change the potential of those streets and address some of Milton’s connectivity issues.

How streets are laid out and how they relate to each other can have an impact on the activities that are possible and appropriate in different places.

Central places tend to be more popular and able to support a range of everyday and secondary activities. Measuring centrality can tell us lots.

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Multiple Centrality Assessment

What is centrality?

There are many ways to be central in the city, and not all places will be central in every sense. This is normal; cities are complex and varied.

Methodology

Streets can be important for a variety of reasons. An easy way to think about centrality is to ask a series of questions about each street. MCA formalises these questions using mathematics and calculates an index containing the precise answers to the questions.

We map the centrality of Milton’s street network using a tool called Multiple Centrality Assessment (MCA).

MCA scores streets according to their potential to be important on three different measures of centrality.

The results are graphically represented using a colour ramp, where streets which show up as red are the most central, and streets which are blue are the least central.

The results of the MCA show the inherent potential of streets to be important within a network. Examining the centrality of the existing network helps us identify strong points, weak points, and suggest ideas for changes to the street network.

We then model these ideas as ‘scenarios’, altering the street layout and putting the new network through

Betweenness Centrality

The input to the MCA is a network of streets and intersections which the software turns into nodes and edges on a mathematical graph. We analyse a network which has Milton at the centre, and a 6km radius of streets from Milton’s boundary. Because we chop the network at its edges, calculations of centrality on the very edge can be biased (‘the edge effect’).

MCA calculates centrality values for each street in the 6km network. When we graphically represent the scores, we divide the scores into 5 groups, each with an equal number of data points, and each with its own colour. When we look at the whole 6km network, the colour of each street is assigned relative to the whole network. When we zoom in on Milton, the colour of each street is re-assigned relative to the range

Straightness Centrality

Do I need to pass through this street to get to other places?

How many places can I get to within a 5min walk of this street?

10mins? 15mins?

Is this street a direct route to other places?

Shops and services of all kinds want to be on streets which people pass through.

Everyday things should be accessible from any street. You might travel further for more specific things. Different scales are important.

The straighter the route from A to B, the quicker you get there and the more places make sense. This tells us something about the legibility of an area.

MCA to see how the changes affect the potential importance of places.

Technical notes

Closeness Centrality

Index for the number of times a street acts as the shortest link between two other streets

Index for the amount of connections a street has within a set distance

Index for the directness between streets

scores within the smaller viewing frame.

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Vehicular Network

Pedestrian Network

The vehicle network forms the backbone of the urban street network. Streets are made not just to be traversed by cars, but also buses, trams, cyclists and pedestrians.

There are sometimes paths and routes which are only accesible by people on foot or bike. The pedestrian network combines the street network with these exclusive paths. Because there are some places where vehicle traffic can’t go, the distribution of centrality on the pedestrian network can be different.

The structure of the vehicle network affects the viability of public transport and the relative convenience of private transport, which affects the shops and services accessible to people beyond the nieghbourhood level.

Analysis of the street network will tell us what streets have high potential centrality.

A place which is central as part of the pedestrian network does not necessarily have the potential to be an important through route or hub in the same way that a place which is central on the vehicle network does. But the pedestrian network can provide a useful illustration of what the potential of the street network might be if it had these extra connections.

A more sophisticated analysis of the pedestrian network could be done which accounts for the presence of pavements on either side of the street network - here we take the central line of the streets in the network as the base.

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Part I Analysis

Existing Network

1km

2km

3km

4km

5km

6km

Existing street network, 6km around Milton

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Balmore Road A803

Betweenness Centrality Do I need to pass through this street to get to other places?

Milton’s betweenness within the wider city context Some streets need to be passed through to get to many other places. These streets have high betweenness centrality, and can be important junctions in cities. Shops and services want to be on these streets; they are places where people are most likely to bump into each other.

Streets are either important places for passing through or not, and not all streets in a city need to be important in this. Street networks usually display a hierarchy in which some streets are more integral to the city fabric than others.

Streets that do have high betweenness are critical and can become the setting for vibrant public life.

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Balmore Road (A879) to the west of Milton and the A803 to the east are good examples of streets which have to be travelled in order to get places. They are important because they connect the north of the map with the city centre, and they aren’t competing with other direct routes. This is particularly obvious in the countryside north of Milton, where these two routes are the only routes into the city centre.

In the city centre there are several key routes which are important in getting between different places.

Broomielaw is a key road linking the city centre with the city south of the River Clyde. Great Western road is a key route linking the city centre with the West End.

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Milton’s betweeness within the local context: vehicle network

The bare bones of the city

In the west of Milton, Birsay Street and the western end of Liddesdale Road along with Castlebray Street (fig.

1) have relatively high betweenness as they form essential routes to and from Milton. To the south and east of Milton, Ashgill Road and Colston road heading east are also key routes.

These routes go around the edges of Milton, rather than through. There is no vehicle route going east to west through Milton (Liddesdale Road has been severed from Ashgill Road at the eastern edge, see fig. 3), nor is there a route going directly north from Milton into Bishopbriggs (fig. 2) - traffic is all diverted via Colston Road in the east.

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Vehicular Network

Pedestrian Network

(Fig. 1) On Glentanar Road

(Fig. 4) On Glentanar Road

(Fig.2) From Milton to Bishopbriggs

(Fig. 5) From Milton to Bishopbriggs

(Fig. 3) South of Milton

(Fig. 6) South of Milton

Milton’s betweenness in the local context: pedestrian network The pedestrian network supplements the vehicle network, changing the landscape of betweenness centrality.

Unlike in the vehicle network, Scaraway Road (Milton) is connected to Duncryne Place (Bishopbriggs) by a footpath (fig. 5). Because this is the shortest path between these places and their surrounding areas, Scaraway Street becomes an important street. The pedestrain network reconnects the severed link at the eastern edge of Milton (fig. 4), providing an east-west through route with the potential to be important.

Without the additional pedestrian paths, the road looping the industrial estate does not serve as a through route. Adding paths in, it has the potential to be an important route to the south-west of Milton (fig. 4 compared to fig. 1).

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Closeness Centrality How many places can I get to within a 5min walk of this street? 10mins? 15mins?

Milton’s global closeness within the wider city context Everyday things should be accessible from any street. But the city operates at different scales depending on what a person is trying to do. Closeness helps us think about the impact of urban block size and how this relates to and interacts with neighbourhood centres, district centres, and beyond.

Global closeness measures the proximity of each street to all other streets in the network.

Local closeness measures the proximity of each street to other streets within a defined radius, each of which represents a certain city scale.

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We have set up our model with Milton in the geographic centre, but as expected, the highest levels of centrality are found within and surrounding the city centre where the vast majority of streets and connections are. Milton is on the limit of the built up area. However, some parts of the city which are of a similar physical distance from the city centre, such as the West End, have higher levels of closeness centrality. This is because the connections between the West End and the city centre are much denser than the connections between the city centre and its urban periphery to the north.

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Vehicular Network A neighbourhood can be seen as the smallest building block of the city, within which you would expect to be able to satisfy basic everyday needs and access public transport. 400m closeness is a proxy for these building blocks.

Areas with high neighbourhood closeness are clustered around the city cetnre and West End, where the street fabric is dense and interconnected.

400m Closeness Centrality

Within an 800m radius (around a 15 minute walk) you would expect to find a broader range of services, perhaps a larger supermarket and more specialist shops.

Closeness at this scale is even more concentrated and still clustered around the city centre. There are very few centres of district closeness outside the city centre.

800m Closeness Centrality

Milton’s closeness on a neighbourhood scale (400m): vehicle network At a 1200m radius, there is still clustering of closeness around the city centre, although there are a few areas to the north east which show the potential to be more regional centres.

Of course, the potential for a place to be a regional centre depends on the existence of smaller city building blocks dense enough to support sufficient population and public transport.

You might expect an area the size of Milton to have several neighbourhood centres.However, the only area of Milton with good closeness at a neighbourhood scale is the grid of residential streets in the north west (fig.

7). It is dense enough that all streets are in easy walking distance.

The amount of connections in this grid improve the closeness of the area to the east, including the portion of Scaraway Street which faces the Skerray Street shops, and the portion of Eglisay Crescent which intersects with Scaraway.

The whole of the east and south of Milton (fig. 8) has very low closeness centrality at the neighbourhood scale. There are long roads with few connections, meaning a limited number of other places can be reached within a reasonable walking distance, even when pedestrian routes are included (fig. 10).

(Frey (2005), Designing the City, Ch3) 1200m Closeness Centrality 18

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Milton’s closeness on a slightly bigger scale (800m)

Vehicular Network, 800m

Pedestrian Network, 800m

Vehicular Network (400m)

Pedestrian Network (400m)

(Fig. 7) Residential Grid

(Fig. 9) Residential Grid

(Fig. 8) From Milton to Bishopbriggs

(Fig. 10) From Milton to Bishopbriggs

Mostly, pedestrian and vehicle networks coincide. The pedestrian network tends to be pavements at the edge of vehicle routes. But just as some routes can only be used by vehicles - motorways, for example - some routes can only be used by people on foot or bike.

Separating the pedestrian network from the street network was particularly in vogue during the 1960s-1980s, and a confused version of this philosophy can be seen in parts of Milton. The intended fronts of the housing in the 1960s gridded area in north west of Milton face away from the street network and towards a pedestrian network.

In other parts of Milton, there are some streets blocked off with bollards so that only pedestrians can get through, and several pedestrian-only formal paths between areas. Canal towpaths are not made for vehicles and have the potential to provide pedestrians with another set of connections.

If we include the pedestrian-only routes in the closeness analysis of streets at an 800m raidus, much more of Milton is accessible. The closeness of the north west of the network extends east covering the tower blocks and most of Scaraway street.

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Bishopbriggs

A803 Balmore Road

Springburn

Straightness Centrality Is this street a direct route to other places?

Glasgow City Center

Milton’s straightness within the wider city context

Straighness Centrality measures the directness of a place.

A place with high straightness has many direct routes and is accessible from other places through paths that are more likely to be linear and direct.

The straighter the route from A to B, the quicker you get there and the more places make sense.

This can help you to find your way and reduce travel time around complex city networks.

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You can see the difference between the historic city street network and later developments. Milton is within an area that is much less directly connected with other areas than the city centre is with its immediate surroundings.

The highest straightness is found in the city centre and other areas where there is a fairly simple grid structure, enabling efficient journeys between streets.

The street network north of the city centre is much more convoluted. The A803 is a fairly direct route which runs to the east of Milton heading south through Bishoppbriggs and past Springburn into the city centre, but there is only one single connection into Milton via Colston Road.

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Milton’s straightness in the local context: vehicle network Milton has lower straightness than most of its surroundings. Colston Road to the east going out of Milton (see close up fig. 12) has high straightness centrality. Balmore Road to the west, and Ashfield Street to the south are also reasonably direct routes. While the residential grid in north west Milton has very good closeness centrality, it does not have good straightness: it lacks direct connections to other places on 3 sides.

The majority of Milton, particularly around the middle, is lacking in direct routes. This is quite clearly illustrated by current bus routes through and around Milton.

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How a lack of straightness might affect transportation The viability of public transport and the form that transport takes is affected by many factors, one of which is the straightness of the street network.

There is almost universally low straightness centrality in Milton. This, combined with the lack of an eastwest through route and other features of the street network, means the only bus between Milton and the city centre is forced round a convoluted route. The street network also means everyone is much further from the nearest bus stop than they would be if routes followed a more regimented structure. You can see the contrast to the east of Milton. The junction between the Kirkintilloch Road (A803) and Colston Road has high straightness: it is legible and clearly allows a for much more legibile bus route.

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Vehicular Network

Pedestrian Network

(Fig. 11) On Glentanar Road

(Fig. 13) On Glentanar Road

(Fig. 12) From Milton to Bishopbriggs

(Fig. 14) From Milton to Bishopbriggs

Milton’s straightness in the local context: vehicle network Straightness centrality is generally improved when we include formal pedestrian paths in our analysis.

The straightness of the residential grid (fig. 13, compared to fig. 11) is improved by the paths which link it with the industrial estate the south, and the canal towpath going down to Lambhill. Straightness is also intensified in the east of Milton connecting to Bishopbriggs (fig. 14, compared to fig. 12).

Even with the extra pedestrian paths, central Milton still has fewer direct routes than Milton’s edges.

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Kernel Density on Betweenness

Kernel Density Kernel Density on Closeness Centrality (400m)

There are two key reasons to use Kernel Density Estimation.

First, KDE captures the idea that the effect of central street space is not just limited to the line of an individual street. To some extent a street’s centrality is experienced in adjacent spaces and nearby streets, with the intensity of this centrality decreasing as you get further away. Where two central streets meet, KDE emphasises the prominance of that intersection: the importance of each central street is multiplied where it meets another central street.

KDE also can be used in spatial anlaysis to show correlations between street centrality and a range of different social, economic and environmental factors. If something can be mapped in space, it can be compared with centrality in the same space, which could be hugely important for planners and others interested in how street structure can be related to urban sustainability.

Technical note: KDE works by dividing the map into a grid. From each street in the network it then searches within a defined radius and takes the average of centrality scores of streets within that radius. For this analysis, we searched within a 200m radius.

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Kernel Density on Closeness Centrality (800m)

KDE on betweenness centrality emphasises just how much Milton is ‘bypassed’. 400m and 800m local closeness emphasise how the south of Milton lacks any dense network of streets which might support a neighbourhood centre. Notice how the centrality at the intersection of Colston Road and Kirkintilloch Road east of Milton is emphasised in all measures, demonstrating the potential of this intersection to be a ‘central place’. All the areas with good closeness more or less spread out from areas with high betweenness - except the residential grid in north west Milton, which is not on the way to anywhere.

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Current Network

Proposed Network

Scenario 1 - reconnect Liddesdale Road East to West

Isolation

Links to wider network

Scenario 2 - Intensify the street layout in South Milton

Part II Scenario

Proposed Network Racetrack

Tight knit

Scenario 3 - Knit together East Milton and Bishopbriggs

Analysis of the current vehicle and pedestrian networks, literature around city strucutre and a look at Milton’s history highlighted a few key areas where making small changes would clearly alter the distribution of centrality in and around Milton.

The scenarios shown have not considered any physical or practical constraints; they are crude changes which illustrate how the centrality of the network can be altered.

Disconnection 30

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Reconnection to neighbourhood Sept-Oct 2016 Network Analysis of Streets

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Scenario 1 Reconnect Liddesdale Road East to West

Betweenness Centrality

Liddesdale Road is reconnected with Ashgill Road at the eastern edge of Milton.

This creates a route through Milton linking the A803 to the A879 (Balmore Road)

Before Milton was developed in the 1950s, what is now Liddesdale Road connected Milton directly Ashgill Road in the east.

Current Network

For some reason, when Milton was planned and developed, this link was severed and Milton was isolated.

Milton, 1910 street layout

As the betweenness centrality analysis of the current network (page X) showed, this means important routes run around Milton rather than through. There is currently no reason or route for someone to the west of Milton to pass through it on their way east.

We saw from the analysis of the pedestrian network that an east-west through route along Liddesdale Road has the potential to make it an important street which might support more activity and urban life.

This scenario links up Liddesdale to Ashgill in the vehicle network, allowing people to flow through.

Proposed Network

The impact of reconnecting Liddesdale Road on the betweenness centrality of Milton is clear and as anticipated: instead of the important routes going around Milton, now the shortest path between places east of Milton and west of Milton is via Liddesdale Road. There is now a practical reason to pass through Milton on the way to other places.

Milton, current (absence of) intersection with Ashgill Road via Liddesdale Road 32

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Current Network

Proposed Network

Straightness centrality

Scenario 2 Intensify the street layout in South Milton

There are small improvements in straightness centrality of Milton as several more direct routes are opened up

A loose grid is superimposed on the area of Milton south of Liddesdale Road in order to make the urban fabric more dense.

Milton south of Liddesdale Road has a particularly sparse street network. In consists of a few long roads with few connections.

Closeness 400m

We saw from the analysis of closeness centrality in the vehicle network that the absence of connections in and around South Milton means it has very poor closeness centrality both at the neighbourhood and larger scales.

There is no real change in closeness at the neighbourhood level

Closeness 1200m

The urban district as agglomeration of neighbourhoods.

(Frey, Designing the City 2005)

By imposing a loose grid on this area, reminiscent of the boundaries of fields before Milton was developed, we are trying to demonstrate how intensifying the street structure might allow the development of a neighbourhood centre with amenities and public transport within a reasonable walking distance.

The fabric of the city as it heads north to the urban periphery is in general less dense and well connected than the city centre. We only model a grid structure on South Milton, but the logic of intensification could equally be applied to the area below, outside of Milton’s boundaries, ‘infilling’ the urban fabric north of the city centre.

Closeness centrality on a larger scale is more focussed in key three areas: the north west of Milton, the south of Milton where it meets the A879, and Bishopbriggs to the east.

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Closeness Centrality, 400m

Current Network

Proposed Network

Closeness 800m

Closeness centrality is also improved at a larger radius

Betweenness

Current Network

The grid has a flat hierarchy: no one road is given more importance than the others. However, betweenness is high on some of the new streets which provide the shortest routes between other places.

Straightness

Proposed Network

Closeness centrality at the neighbourhood scale is vastly improved in the south of Milton with the grid structure. A denser grid would give even higher scores. This demonstrates the potential for new neighbourhood centres to be created by intensifying the existing street network.

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The imposition of a grid improves the legibility of the area and the number of direct routes between places. You can see the contrast between the winding routes above Liddesdale Road and the new rational ones below.

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Scenario 3

Straightness Centrality

Knit together East Milton and Bishopbriggs

Milton is tied in more densely with Bishopbriggs, which borders Milton on the north east.

Current Network

Relevant image number 1

The urban fabric to the east of Milton has been altered to provide additional connections with the neighbourhood of Bishopbriggs. The new connections extend to the west of Ashgill Road, introducing a block structure either side of this route.

On examination of the street network, it is apparent that the east of Milton is poorly connected to neighbouring communities despite its close proximity to Bishopbriggs.

Colston Road, for example, is the only connection between Milton and Kirkintilloch Road, which is a significant approach to Glasgow City Centre. There are, however, existing paths that significantly contribute to the centrality at this location. Evidence of a historic path network between Bishopbriggs and Milton is also evident by the presence of two railway overbridges, which have been made redundant by a 1990s residential development.

This scenario seeks to establish additional connections via the conversion of paths to streets as well as ‘stitching’ together the urban fabric surrounding Ashgill Road. This may be able to encourage the high measures of centrality around Kirkintilloch Road to spill over into Milton.

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Proposed Network Kirkintilloch Road has high levels of straightness as this road forms a relatively direct route to and from Glasgow’s City Centre. Colston Road, which connects Kirkintilloch road with Milton’s street network has a comparable level of straightness centrality. This, however, significantly drops off west of Ashgill Road, which acts to direct traffic around Milton in a somewhat convoluted route.

The new block structure around Ashgill Road has extended the measured levels of Straightness Centrality further into the fabric of Milton, as through-routes connect Kirkintilloch Road with Scaraway Street, Liddesdale Road, and Torgay Street. The levels of Straightness Centrality may be extended further west with additional alterations to the network. The interventions illustrated by Scenario 3 capitalise on the existing centrality of Bishopbriggs and may, therefore, be considered as the Sept-Oct 2016 Network Analysis of Streets 39 first stage of the creation of a more directly connected Milton.

Current Network

Proposed Network

Closeness 400m

Conclusion Scenario 1

The block structure around Ashgill Road exhibits a reasonable level of Local Closeness Centrality at 400m, which suggests that this area is a well-connected and accessible neighbourhood.

Closeness 800m

The block structure retains a good level of Local Closeness at 800m, which suggests that this could be a possible location for a neighbourhood centre. This contention is supported by the high levels of Betweenness Centrality at Colston Road, Ashgill Road, and Liddesdale Road, which suggests that the location is also an important place for passing-through.

Betweenness

The centrality of a street measures its potential to act as a setting for human activities and interactions. The three types of centrality – Betweenness, Closeness, and Straightness measure different types of ‘potential’ to reflect, at least in part, the complex nature of the city.

The resulting mosaic of different potentials provide an account of the busiest streets; the quieter neighbourhoods; the roads that are necessary to pass through; and the places that are difficult to find.

The Multiple Centrality Assessment for Milton, however, has not been limited to providing an account of the potential of the existing environment. Rather, by investigating three possible scenarios, we have shown that changes to the road network can result in a significant redistribution of the centrality of the area’s streets. Quiet places may be transformed into a hives of activity while poorly connected areas can be stitched back together to form viable places.

The additional link over the railway line has high levels of betweenness centrality, which illustrates the previous role of the railway over-bridges as important features for passing through. The betweenness Centrality of Liddesdale Road has significantly increased due to the new connection between this road and Ashgill Road.

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Any strategy, however, needs to be considered carefully to match a street’s centrality with its function. There is little merit in having a farm track with a high measure of betweenness. This potential is unlikely to be realised as the road is unsuitable or unattractive for passing through;.

However by matching future development and centrality (for instance locating neighbourhood centres in highly central locations) will provide the best possible opportunity for the areas success. Everything happens somewhere.

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