In this week, you will be running some simple network analysis processes to examine the catchment area of the Mt Eden train station from a number of perspectives including walkability, cycle commuting and transit connectivity. These – cycling proximity, walkability, transit connectivity – are determinants of the accessibility of the train station. Getting more individuals commuting by public transit is an ongoing initiative of Auckland Transport and Auckland Council. It is environmentally more sustainable, cost effective (depending on distance traveled and passenger per vehicle), and reduces motor vehicle traffic on Auckland’s seemingly always-already congested roads. Rail in particular has the added advantage over buses in that it constitutes its own dedicated route of travel separate from the motorway, which means that once individuals get on a train, they are on a mode of direct transportation in which they do not need to compete with other vehicles (i.e., unlike on a bus, you won’t be stuck in traffic once on a train). With the presence of the Britomart, for example, commuting to work by train represents an efficient and direct means of traveling into and out of Auckland’s central business district.
In their study of the distances that people are willing/likely to walk to public transport in
Brisbane, Australia, Burke & Brown (2007) determined the following:
Burke M & Brown AL (2007) Distances people walk for transport. Road & Transport Research: A Journal of Australian and New Zealand Research and Practice 16(3): 16-29.
And we are going to need these values to answer the questions.
By the end of this tutorial, you should be familiar with:
You can download the template for the assignment below. Please answer all the questions and paste all the produced maps from ArcGIS into the document.
Please save the document as a PDF before submitting.
In this network analysis section, you will be working with the following resources. They are provided in a file geodatabase, which is like a container to store your vector GIS files:
Note: These datasets are provided for use in this lab, and are not to be used for any commercial or other purposes.
This is a separate backup of the bus routes layer if needed.
One of the most basic questions asked of a GIS is "what's near what?" For example:
The Proximity toolset contains tools that are used to determine the proximity of features within one or more feature classes or between two feature classes. These tools can identify features that are closest to one another or calculate the distances between or around them.
Buffer is one of the most important proximity tools and it creates buffer polygons around input features to a specified distance.
For more info on how to use the Buffer tool head back to the pre-lab instructions, or learn more about how Buffer works.
For example, we can use buffer to see how many bus stops are within 500 meters of a train station, to decide a transfer.
The buffer can also be used a quick and easy way to find features within a certain distance of the input, by combining this with another analysis.
We want to know how many people are within the walking distance of Mt Eden Train Station, so after building the buffer layer we can use several different tools to find the answer that I will show you here.
Buffer & Select by Location
This is the quickest a simplest method of finding the population within the buffer (in fact we don't necessarily need to have created the buffer layer to use this)
It is good practice to always clear a selection as soon as you are done with it, as this may mess up the next analysis you do.
Simple Select by Location
You can also select by location without needing to create the buffer.
The next option is the Intersect tool. This creates a new layer that contains only the features you are after. Learn more here.
All of the above mehtods produce the same (or similar result). Which one you choose depends on the work you are doing, and personal preference.
Now that you are an expert in all things location analysis, choose a method, and answer question 1.
What percentage of the total Auckland population, to two (2) decimal places, is potentially served by the Mt Eden train station? Use the 85th percentile distance which people are willing to walk to a train station (Burke and Brown, 2007) on the introduction tab.
Detail step-by-step the procedure you used to determine the estimate (point form or numbered response is acceptable). Then, briefly explain the limitation(s) of using the approach/methodology you outlined.
As a first step, ensure that the Network Analyst extension is enabled (Customize on the main toolbar > Extensions > make sure the box next to Network Analyst is checked).
You can access most Network Analyst functions via the Network Analyst Tools toolbox under ArcToolbox, but you can also add theNetwork Analyst Toolbar (Customize > Toolbars > Network Analyst).
Clicking on the
Network Analyst Window icon will open a separate window that contains all your network analyst ‘work’, and helps organize your network analysis operations and layers. You can ‘dock’ this window as part of the ArcGIS interface (move it into one of the blue arrows that appear either along the top, bottom, or right/left sides of your screen to place it in that location). (Note:This may not be possible using ArcMap in FlexIT - just move the window to the side of your screen).
Usually, when a network data (e.g., road network) has been added, you must build it by clicking on the ‘Build Network Dataset’ icon. However, in this case, the network has already been built (the roadnet_ND layer that appears in the dropdown of available network datasets).
You can add new network analysis layers (i.e., new network analysis ‘problems’) either through Toolbox or via the Network Analyst dropdown on the far left of the Network Analyst toolbar. If you choose to add a new ‘Vehicle Routing Problem', for example, this will add a new layer to your table of contents, as well as new items to your Network Analyst window (with 0’s in brackets next to these as you haven’t specified any network locations yet). Once you have specified all of your inputs (defined the problem), you can ‘Solve’ the network problem by clicking the ‘Solve’ icon on the Network Analyst toolbar.
With the ArcGIS Network Analyst extension, you can find service areas around any location on a network. A network service area is a region that encompasses all accessible streets (that is, streets that are within a specified impedance). For instance, the 5-minute service area for a point on a network includes all the streets that can be reached within five minutes from that point. Service areas created by Network Analyst also help evaluate accessibility. Concentric service areas show how accessibility varies with impedance. Once service areas are created, you can use them to identify how much land, how many people, or how much of anything else is within the neighborhood or region (ArcGIS Desktop Documentation).
Determining the estimated number of people within reasonable walking distance of the Mt Eden train station is a service areaproblem. As such, add a New Service Area via the Network Analyst dropdown on the toolbar. In so doing, you will also see a new, complex multi-element Service Area layer added to your Table of Contents, as per the diagram below.
At this stage, Facilities are the input of concern. Right-click on Facilities and select Load Locations. This will open up the Load Locations dialogue (below).
Because this is a simple problem at this stage, you need only load the Mt Eden rail station (either from the Train_Stations layer or loading the train station itself if you have written it to its own layer).
Once you have loaded the Mt Eden train station, as you can see from the screenshot mosaic below, there has been 1 network location added to Facilities; and, as we can tell from the symbology for the Service Area problem layer, it has been ‘located’ on the network (bright green).
Because you want to determine an estimate of the % of the Auckland population within walking distance of the Mt Eden train station, you will want to make sure that these parameters are set correctly. To do so, right click on the Service Area layer to access the layer’s Properties, and openthe Analysis Settings.
In this scenario, we are not interested in road travel time but rather the distance that someone is willing to walk to a train station. Hence, change the Impedance to 'Length', and specify a single Default Breaks value that is the 85th s% walking distance defined by Burke & Brown (2007). Here you could specify multiple break values/distance bands separated by commas (e.g., ‘1000, 2000, 3000’), but for the intents and purposes of this step, use only the singular distance value.
The direction here is not an issue (distance walking to and from one’s home to the train station is the same). Furthermore, we don’t want to use the road network hierarchy (class of road), so uncheck this option. Restrictions such as one-way streets and turns also don’t apply to walking as opposed to driving, so remove these as analysis parameters as well. Click Apply and Ok, and exit the Layer Properties for the Service Area layer.
Solve the Service Area problem. Your output will be an irregularly shaped polygon that represents all areas on the map within the specified walking distance along the street/road network. You will see that the Polygons element in the Network Analyst window is now populated (demarcated by (1)). Use this to come to an estimation of the % of the Auckland population within walking distance of the Mt Eden train station.
Report this value in response to Question 2 for this assignment.
How many people are served by the Mt Eden station when the streets by which people walk to the train station are taken into account? When determining your estimation, specify the spatial relationship as one of intersection.
The following video shows the process of creating a service area:
Multi-Facility Service Area Problems
We are not there yet! You will notice from the output polygon generated in the previous step that the Grafton rail station, which is the station immediately northeast of Mt Eden, is actually located within the Mt Eden train station service area. We can assume that individuals living closer to the Grafton train station are more likely to walk to that train station rather than Mt Eden. At the same time, we should probably account for the fact that individuals living in the southwest of the Mt Eden catchment (service area) may similarly be closer to the train southwest of Mt Eden, Kingsland. This constitutes a multi-facility service area problem. To determine the population for whom Mt Eden is closest (i.e., for whom Mt Eden is closer than either Grafton or Kingsland), we need to define the problem differently.
Insert (paste) your screenshot of the Polygon Generation settings of the Layer Properties dialogue for the multi-facility service area problem for the Mt Eden train station.
What is the number of people served exclusively by the Mt Eden train station, where Mt Eden is the nearest train station within reasonable walking distance (85th %) and where walking distance has been minimized to other nearby train stations (Grafton or Kingsland)?
Finally, create a map to display your final multi-service area as Map 1.
Map 1 should show the pedestrian catchment for Mt Eden Train Station. The map should tell the story of where the walkable areas are, why they are there specifically, e.g. using the roads, train station layers etc to add context.
Add the meshblocks layer as the background to the map, and symbolise this by population density (this is already a field in the meshblocks layer).
Rememeber to avoid clutter on the map - roads should be symbolised in a subtle way, and thinks like bus stops, routes or cycle paths should be turned off for Map 1 as they are not relevant.
Map 1 is a great opportunity to explore some of the advanced symbols available in ArcMap for point features.
This is also a good time to have a look at labeling. In your maps it makes sense to show all the train stations, or at least those nearby, but Mt Eden needs to stand out as it is the main focus of the analysis. This could be accomplished by making the symbol different, a different color, larger etc.
You can also do this by labeling.
Labels are a great way to add context, and they are also a great way to clutter up a map (e.g. if you added a label for each road!). Use then sparingly - do all the train stations need to be labelled, or just the key ones?
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Location-allocation involves determining which locations (e.g. facilities) from a set of potential locations serve demand for those facilities in ways that minimize impedance (e.g., travel time along a network). More information on location-allocation can be found online.
Here is a simple problem that can be solved through a location-allocation analysis in this study: which of the 50 train stations minimises overall travel from all 5,656 bus stops in the Auckland region? In other words, which of the train stations is a travel-time weighted centre to which travel time from all possible bus stops is lowest?
You may get a warning saying not all locations could be allocated. This is OK to ignore - the issue comes from bus stops on Waiheke Island not being connected by road to any train station. Your output will be lines added in the Location-Allocation layer connecting all bus stops to the one facility (train station) to which travel along the network is minimized from all possible demand points (bus stops). Granted, this does not take which portions of the road network are actually served by bus routes into account; however, the bus routes layer is not a network dataset. You could attempt to build one; however, the reason we are using the Corax road network is that building a network dataset is extremely time-consuming in terms of processing time and error-prone (ArcGIS is likely to crash). Hence, this is not an ‘exact’ analysis in this case, but rather a hypothetical one – and an introduction to the tool.
The selected facility will be selected and the ‘chosen’ facility and will appear differently symbolized. You can also determine which of the train stations has been selected via location-allocation analysis by opening the attribute table for the lines.
By doing the location-allocation analysis, try to answer the following two questions.
To which train station is travel time from all bus stations in the Auckland region minimized, as determined by simple location-allocation analysis? (Hint: look at the locations in the Network Analysis window - one will be marked as chosen)
As a final step we want to see which bus stops in the network feed each train station. This would allow us to find the most efficient route if a journey involved a bus leg and a train leg to reach the destination.
A warning will appear that informs you of the train stations that cannot be allocated any bus stops. Hit OK to ignore this warning.
Taking all the train stations within the Auckland region into consideration, and using the road network hierarchy, how many bus stops are allocated to the Mt Eden Train Station on the basis of minimizing impedance (again, not taking actual bus routes into consideration, just the bus stops)?
To find the number of lines you could count them manually, but there is a quick and easy way to do this.
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Advanced Network Analysis
Now that we have learned the basics of network analysis, we can move on to the main assignment part of this lab. We are going to explor how Mt Eden train station serves people around in terms of walking, bus, and cycling. For each part, we are going to assume that someone near Mt Eden is getting the train into Britomart to go to work (those were the days ...).
We have already found the area where people might resonobly walk to Mt Eden train station (Map 1), but what about other modes of transport? We will also look at areas where you could take a 15 minute bus ride to the station, or a 15 minute cycle ride. We will go through the bus catcment process together, then you will tackle the cycle cathcment after.
Based on some stats, we are going to assume that people ould be willing to take a 15 minute max bus ride to get to the train staion to finish their journey. In addition, the data from Burke & Brown (2007) shows us most people are willing to walk 400 m to their nearest bus stop. Therefore we are going to find areas within 100 m of a bus stop that is served by a route that is 15 mins or less to get to Mt Eden station. Lets get started!
Next we will do a bit of detective work to find out which bus routes go past these stops.
Next we will find all bus stops along these five routes
The bus routes layer shows the centre-line of the bus route. We can assume that most bus stops along this route will be located near this centreline, within 10 metres.
The output of this operation is all the bus stops served by the five bus routes that run past Mt Eden train station
Next, we want to narrow this down to only those stops within 15 minutes drive of Mt Eden station.
The output is a polygon that shows areas within a 15 minute drive of the train station. This is a suspiciously large area, but that is due to assumptions that there is no traffic, and the vehicle can drive at the speed limit, with no other impeding factors.
There we have it! All the bus stops within 15 minutes of Mt Eden Station. We know from Burke & Brown (2007) that the median distance people are willing to walk to get to a bus stop is 400 metres
We're nearly there! All that's left is to tidy up the area a little. We are going to assume that anyone who lives within the walking catchment we created earlier will walk to the train station, rather than get the bus, so we will remove this area from our bus catchment.
The output is now the areas within a 400 m walk to a bus stop that is within a 15 m ride to Mt Eden station. As we are modelling someone travelling into the central city, the areas to the north of the station do not make sense, as people living here likely would not get a bus to Mt Eden, just to get the train back into the CBD. Therefore, we will tidy our data by removing these areas.
Note: if the button for 'Explode Multipart Feature' is greyed out, try clicking 'Stop Editing', save the document then try edit the layer again.
There we have it! We have now found areas that are served by a 400 m walk to a bus stop that is a 15 min ride to Mt Eden station, excluding areas within the walking catchment, and areas already close to the central city. This layer will form the basis of your Map 2, but make sure to provide context to the layer (e.g. the train stations, relevant bus routes and stops). Remember the key point of a map, it should tell us where the bus areas are, and show why they are here. Remember to keep the map tidy and not too cluttered.
As part of the write up for the maps we want to know the total number of people served by Mt Eden station, between walking, bus and cycling. It makes sense to find the bus number now, by using either Intersect or Select By Location on the centroids layer, and the final bus catchment.
Map 2 should show the bus commuter catchment to Mt Eden train station. You should also include the relevant bus routes, bus stops etc. Mt Eden station should be shown prominently. Add the meshblocks, symbolised by population density.
Head to the symbology tab, and have a look at all the different point symbols available (try search for "train").
Include some write-up that mentions the following:
The final task is to find areas within a 15 minute bike ride to Mt Eden station, using a few key assumptions. There arent any instructions for this section, instead using the skills and tools you have learned in the last section, and the below key criteria you should be able to derive the cycling catchment.
Make sure you write down the steps you took as you go, as this will be part of the writeup, and also helps if you need to go back and figure out what you have done earlier!
Finally we will find the area that people may cycle to Mt. Eden Station to catch a train, using a few assumptions.
The entire process can be generalized as follow steps:
Map 3 should include the service area and the reasonable bike paths, along with any other layers that add context. Again, add the meshblocks symbolised by population density, and Mt Eden Station.
When it comes to finding the total population that is served by Mt Eden Train Station by walking, bus and cycling, you could just simply add the three percentages you have found for each of those catchments together to give a rough estimate of the population.
A more statistically sound method that removes overlap between the three catchments is to merge them together and use this to find the population. The necessary steps are summarized below:
The Editor Toolbar
You can make heads-up (interactive/on-screen) changes to spatial geometry. For example, you can split polygons and delete portions of areas (or split lines, delete points, etc.). This may come in useful when working with the ‘reasonableness’ criterion for cycle commuting in your analysis (you may want to delete parts of this service area polygon). This is done using editing tools.
On the Main Menu, go to Customize > Toolbars > Editor. This will bring up the Editor toolbar:
To make edits to a layer, on the toolbar, click on Editor with the dropdown arrow highlighted above.
Note: If the 'Cut Polygons Tool' is greyed out, or gives an error message when clicked, click 'Stop Editing', save the ArcMap document, and start editing again.
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Tips & Tricks
Map 1 does not require a write-up - the assginment template asks for a description, just ignore this.
Default Geodatabase issues (if working with FlexIT)
The initial Default Geodatabase can become corrupted (the "Unable to create or open Default Geodatabase" error. ArcGIS unavoidably always want to create/use this when starting up), so the following would need to be done:
Buttons on the Editor toolbar are greyed out
Try clicking the 'Editor' toolbar, 'Stop editing', saving the ArcMap document and trying to edit again.
Some tools are failing, saying they 'cannot access the data'
This forces ArcMap to process in the foreground (you will see a progress bar while it is working) which often fixes data compatibility issues. This can get annoying, so you can turn background processing back on once the failing tool has worked.
Launching ArcMap & H: Drive Acess
There has been some issues, but they should be resolved now. Read the instructions on the 'Getting Started' tab first - these should prevent any errors.
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