In a previous post, we talked about how to perform a vacation of an ally or right-of-way parcel using the parcel fabric data model in conjunction with the Local Government Data Model and the Tax Parcel Editing Template from the resource center. For this post we are going to talk about the same process, but without recreating the original lots. As with the previous post, we will be working through an example provided by the City and County of Denver. For this example, the lots currently in the database do not match the legal description (the lots should all be 125 X 25), which is a common occurrence in most databases.
Performing the Vacation without re-creating the original lots
Using the existing lots is the easiest and most straightforward way to go, but not the best-practice. You could think of this as the quick-and-dirty way to get the tax parcels added and move on with your day.
1. Begin by creating a connection line for the gap between the two disconnected groups. Use the tool on the Parcel Editor toolbar. This ensures that a construct from parent process will work, since it requires the group to be connected.
2. Use the parcels on the northernmost part of this group, across the gap (alley). Note the 29’ distance and 87 degree bearing. The distance measurement should be 30’, with a bearing closer to 90 degrees. Since we are going with the current set of lots, though, we will simply hit the Apply button to use these numbers.
3. Select just the Tax Parcels that you need to extend to the center of the ROW (Alley) being vacated, right click and select the Construct from parent option.
4.Select the Segmented Line Tool at the top of the Parcel Details window.
Create a two part segmented line over the top of the connection line that you created. Take note that the lines as inversed are 14.515ft, not 15. This is due to the lots/parcels not being repaired prior to the edit.
Note: Be careful, there are two points very close together 81 & 121 in this data.
5. Same for the southern edge, connecting the midpoints together with another boundary line, to form a centerline running down the middle of the alley/ROW.
6. Next step is to create lines across the construction lines used to re-create the ROW (Alley) and the centerline.
a. Start at point 116 as shown here and then place the cursor in the Bearing field
b. We want to extend the parcel line along the same bearing, so move the cursor to snap to the tax parcel line that you want to pick up, hold SHIFT and then click to pick up the bearing (this will populate that value in Bearing field).
c. Purposely type in something longer than 14.5 (1/2 way point or ROW width)
d. Use the Planarize command to break the line at the centerline. Select the overlapping piece in the grid, right click and choose the Delete Rows option to remove it.
7. Continue this process until all the remaining tax parcels have been extended to the ROW (Alley) center and then merge the smaller pieces to you existing tax parcels to get you final output. In this example, there are no historic ROW parcels created, since they were not there to begin with.
Content provided by Larry and Chris (Parcel Editing Team)
The parcel fabric data model lends itself to many improved workflows for managing your parcels, particularly when it is used in conjunction with the Local Government Data Model and Tax Parcel Editing Template for ArcGIS 10, which you can download from the resource center. Some of these improved workflows are hard to detail in the help, though, so we’re hoping some blogs will help out. One of these workflows comes from the City and County of Denver and centers on how you perform a vacation of an alley or right-of-way parcel. The City and County are using the Local Government Data Model, which provides the ability for managing not only parcels, but also Lots and Subdivisions.
There are a few things to consider before performing an
alley vacation or creating any new parcel(s).
1. Does the alley exist in the lot layer?
If the alley exists, the first step
before doing any work would be to make sure the original lot (alley) is marked appropriately
in the historic layer (marked as Vacation).
2. How accurate are the measurements on the
adjacent block edges/lots?
In the data that was used for this
example, the lots should be 125 feet by 25 feet, but a look in the parcel
description shows the measurements are off for some of the lots.
The best practice in this case is to
re-enter the original blocks by cogo-ing the outer boundary of the block from
recording, and then using the Parcel Division tool or Construction to recreate
the lots. Once completed, these blocks can be joined to the Fabric using
control points or even orthophotography.
Of course, the tax parcels would also have to either recreated from the
lots or re-joined to fit the newly constructed lots.
The first workflow listed below can be used
for this task. In a later post, will
talk about how to complete this process without recreating the lots.
Recreating Blocks and Lots from Records (original city subs)
1. Mark original lots historic or delete them all
together from the Fabric. In this example,
I’ve left this step until the end so that I can use the lots as reference to
name the new ones
2. COGO entire block boundary from record. For this example, all of the lots are 125 X
a. Create a new Plan, and give it an appropriate
b. Create a new construction inside that plan, set
the parcel template to “lots”
c. COGO the outer boundary like this:
Please note that the alley was divided two pieces. More on that later. Also note that the original lots are displayed in the background.
d. Delete the 575’ measurement
e. Select the Segmented Line Tool from the top of the Parcel Details window:
To start, make sure you cursor is in the FROM cell of the next available row and click in the grid to replace the NW corner, type “23” to get 23 equal segments or right click.
f. Click the SW corner, and do the same thing for all the other edges.
g. Digitize in the connect lot lines, create a connection line for the center of the Alley.
3. Build and Join. For this example, the parcels are turned off and we joined directly to photography as control. Later on, the data can be re-adjusted to proper control if desired.
a. Then create any join links between the existing Parcels and the new lots…make sure to have points turned on for this!
b. Hit OK, and the data will now look like this:
4. This will make the ROW (Alley) Vacation easier since you now have the centerline of the ROW (Alley) to use to expand the tax parcels.
a. With the Tax Parcels and just the ROW (Alley) in question selected, we can use the Construct From Parent option to do the rest of the line work.
b. We can digitize over the connection lines, creating new lines that extend the current tax parcels. The Planarize command can be used to get rid of any excess. We then build to create polygons and merge the smaller vacation leftovers to the current tax parcels, carrying their attributes over to the newly expanded parcel.
c. Finally, mark ROW (Alley) Vacated (Historic).
Content from Larry and Chris (Parcel Editing Team)
6. Trace edges when cutting polygons.
The current park design is landscaped with shrubs along the entire western border. However, I want the area to be three different types of vegetation, each separated by a foot path. I draw features for the new path lines first so I can use them to split the large polygon. Then, I select the polygon and click the Cut Polygons tool, change the construction method to Trace on the Feature Construction toolbar, and follow along the edge of the overlapping foot path feature. I need to make sure that the trace goes all the way across the polygon so the cut is successful. When I finish the sketch, the polygon is split and its edge exactly matches the shape of the path.
Another method I can use to split the shrub patch polygon by the overlapping foot path line is to snap to the edge of the polygon, right-click directly over the foot path line, click Replace Sketch, and finish the sketch. Replace Sketch pulls the shape of the underlying feature into the sketch used to cut the polygon.
7. Change attributes for multiple features in the Attributes window.
With the shrub patch polygon now split into three features, I want to make two of them flower beds by using the Attributes window to change the landscaping type. To update just two of the three selected polygons, I hold down CTRL and click the feature entries (listed by display expression) at the top of the window, then change their landscaping from Shrub Patch to Flower Bed. If I click the layer name, all selected features are updated; clicking just one feature updates just that feature’s values.
8. Extend lines by sketching with the Continue Feature tool.
The new foot path across the western landscaping needs to be extended eastward across the open space so it connects with another foot path. I can use the Continue Feature tool to extend a line by drawing a sketch. Since the path was digitized from the west originally, I flip the direction of the line so it will be extended toward the east instead. Continue Feature is available starting with ArcGIS 10 Service Pack 2, but must be added to a toolbar from the Customize dialog box because it is not on the default user interface.
9. Use Find Text to provide the text for annotation.
With my park features placed on the map, I want to add some annotation to describe them. To make the text string for a new annotation feature come from the attributes of an existing feature on the map, I can use the Find Text tool on the Annotation Construction window. For example, I click Find Text, click a recreational polygon, and it populates the text box with Athletic Field from the attributes of the polygon. This saves me from typing words manually.
10. Use the Topology toolbar to update multiple features at once.
I want to expand the area of vegetation around the recreational area so it goes closer to the eastern sidewalk of the park. This edge is shared by flower bed polygons, a foot path line, and open space polygons. I can build a map topology to make edits to all these features at the same time, including moving edges, reshaping edges, and modifying the vertices on the edges. I select the shared edge with the Topology Edit tool and use the Reshape Edge tool to update simultaneously all the features that share the common boundary.
The Shared Features window lists which features are part of the selected edge. By default, all shared features are updated when an edge is modified; I can exclude features from edits by unchecking the boxes next to the feature. Once I reshape the edge, the features are still coincident.
If I attempt to perform this edit with the Reshape Feature tool on the Editor toolbar, only one feature is updated at a time and gaps and overlaps will form among my features. With Reshape Edge, they are all modified together. Be sure to use the topology editing tools when making edits to features that share edges.
Content provided by Rhonda from the Editing Team
3. Set a feature template’s default attribute values.
Park analysis and design: Sketching the design of a new park (part 4)
In my previous blog post, I used a voting application allowing citizens to vote on their favorite location for a park based on choices derived from a suitability analysis. Using ArcGIS Server, their choices went into a database and allowed the parks to be ranked based on their popularity. We have a winner, so now our task is to design the new park. Continue reading
Park analysis and design: Voting on a new park location (part 3)
In my previous blog post, I determined suitable locations for a new park by analyzing a series of datasets provided by the City of Redlands. The final output showed a number of parcels that matched the standards established in the model. The next task is to seek feedback from the public. To do this, I’ll take advantage of a web application I developed using ArcGIS Server.
Preparing the data
The park suitability model resulted in an output of a feature class containing many multipart features. A multipart feature, as the name suggests, is a feature with multiple parts. Think of Hawaii as one feature (state) with multiple parts (islands). To break the suitable areas for parks into separate features, I’ll use a tool called Multipart To Singlepart.
With every parcel being its own feature, I can calculate the area for each potential site by creating a field and using Calculate Geometry in the attribute table. Once I have the area in acres, I need to convert all the polygons to points using the Feature to Point tool so I can represent each park as a point location in the web application.
The final dataset contains fields for the park’s area and an identification number, which I derived by copying the OBJECTID to a field called ParkID. This number is used to link the park feature to the voting results table, which also has a field for the ID named ParkIDVoted (so I can distinguish it in the Flex code).
Building the web service and application
I’m developing my application using the ArcGIS API for Flex, so I first check if there are any existing samples that I can use as a starting point to help me collect votes. I find the Editing a related table sample, which demonstrates a similar scenario that I can modify for the needs of my own project. This sample takes a set of incidents (stored as points) and allows the user to flag an incident as important. In the code, there’s a map service that holds the points, as well as a table to hold the results. In the geodatabase, these are linked using a relationship class. These datasets need to be in an ArcSDE geodatabase with feature access enabled to allow web editing. Accordingly, I can set up my data this way and publish it with ArcGIS Server, which makes the parks and the table become layers in a map service.
I need to change a few things in the sample to customize it for my own application: the URL of the parks layer and the URL of the table holding the votes. Some field names are different, but other than that, the logic of casting the vote is fairly straightforward.
In terms of the interface, the sample shows how to use the pop-up window (infoWindow) when a park is clicked. I used the same thumbs-up icon and added a bit more information to the information window. Additionally, I published the park access map and the final suitable parcels layers, which can be turned off and on in the application using simple Flex components.
Submitting a vote
When users find a park they are interested in, they click the icon on the map. This sends a query to the server using the x,y location of the map click, which also triggers a relationship query that gets the number of votes of the record in the related table. The infoWindow then displays the ID of the park that was clicked, the park size, and the total count of current records in the related table, which are votes in favor of this location.
To vote for this park, the user clicks the thumbs-up icon, which sends a message to the server (applyEdits) that puts the ID of the park, plus a value for “like” into the related table through the relationship class. The count is increased by one and the total vote count can be seen immediately.
Counting the results
On the server, the related table collects the votes. Each record in the table is a vote, which includes the Park ID the user clicked, an attribute for the vote (“true”), and the date of the vote.
When the voting period is over, I can run a summary on the final table using the Summary Statistics tool. This counts the number of records with the same ID and creates a table, which I can then build a report on using the new reporting tools in ArcGIS 10.
Now that I have a winner, the next task is to design the park using the sketching tools in ArcGIS 10. I will cover this in my next blog post.
Accessing the Data
The data, Flex source code, report template, and a few other parts of the workflow can be found here
The rest of the data and tools for this blog series can be found in the Park Analysis and Design group (make sure to filter by Show: All Content at the top of the page)
Content for the post from Matthew Baker
In my previous blog post, I analyzed park accessibility in the City of Redlands and discovered several areas of the city that were farther than one mile from an existing park along the walkable street network. Now, I want to determine where to best locate a new park within the areas I identified as being underserved by current parks.
To answer this question, I’ll conduct a suitability analysis to find parcels that are most appropriate for a new park.
There are two main types of suitability analysis: binary and weighted. Binary suitability analysis involves a binary final answer —1 or 0, or in our case, suitable and unsuitable. A weighted suitability analysis allows for a range of final answers, from 1 to 10, for example, and allows certain layers to have more influence (weight) on the result of the model. For this example, I’m going to create a binary suitability analysis model.
As with our park accessibility analysis, I’ll start with several datasets from the City of Redlands, including parks, schools, roads, trails (off-road and on), existing and proposed bicycle lanes, and vacant parcels. Before I construct a model, I should know the distances the new park should be from certain features. In most cases, I’m looking to be close to certain features, but in other cases, I want to make sure I’m far enough away, such as with highways and existing parks.
Remember that any of these values can be changed to suit any criteria. ModelBuilder allows a workflow to be created, run, and then modified to suit different ideas of how far each feature should be from a new park.
Creating a data processing workflow
My analysis should read like a flowchart: buffer the schools, trails, and bicycle lanes to make the ‘good’ areas. Buffer the existing parks and highways to make the ‘bad’ areas. Then remove the bad areas from the good areas, and find the areas that are common to the vacant parcels.
Developing a suitability model
To use the data and tools found in ArcGIS to accomplish suitability analyses, I’ll develop a model using ModelBuilder. ModelBuilder acts much like a living flowchart, with data elements connecting to tools creating outputs just like the flow processing diagram. A model serves not only as an organizational tool for doing data processing, but the elements of the model store parameter values and data paths that can be changed, and the model itself can be shared and run on different data. For example, other users can change the input datasets to their own parks and street network to achieve the same analysis.
By definition, geoprocessing tools take one or more pieces of geographic data, run a process based on parameters I define, and create a new piece of data as the result. That first result can be fed into another tool which results in yet another piece of data. Once the new data has been created, the old result can be discarded. This data is called intermediate data. Each piece of intermediate data should be written to a scratch workspace, which is defined in the environment settings of the map or model. Keeping intermediate data in a scratch workspace is a great way to ensure I don’t end up with random datasets all over my computer.
Tools for models can be found using the Search window. The Search window will allow me to type in the name of a tool, dataset, or script and show results across all types of data. To add a tool to a model, drag the tool by its name, and drop it on the model canvas. Model elements can be connected using the Connect tool from the model window. Double-clicking a tool or element will open a dialog box that allows me to ensure the settings are correct before I run the model. ModelBuilder will also check the inputs are valid before running, and I can check them all manually by clicking the Validate Entire Model tool from the ModelBuilder toolbar. I can save the model in a toolbox, which can be stored anywhere on disk or in a geodatabase, as I am doing.
When the model runs, a dialog box shows me the progress, notification that it is finished, and any messages, warnings, or errors that might have occurred. The Results window is the location to track the status of a model or other geoprocessing operation.
Reusing models as tools
Another nice feature of models is they can be used in other models as tools. Since I already proved the effectiveness of measuring distances along the road network versus straight-line buffers, I can take the method I developed and use it as a tool in my park suitability model. I’ll call the tool Buffer Along Roads and use it for the schools and existing parks, which are the only datasets that require travel to be measured along the road network.
My model tool will operate as any other tool: it requires an input point dataset and will create a polygon dataset containing buffers along the roads using the distances exposed in the reclassification scheme. Once I’ve created these distance polygons, I then choose the ones that meet my criteria—in this case those that are ½ mile from existing parks and within ½ mile of schools. From there, the rest of my analysis can continue using straight-line buffers from bike lanes, trails, and highways.
Determining the final location
When the model is finished, I see that there is more than one suitable location for a new park. I then have some work to do to figure out the final parcel or location. For example, perhaps I’m looking for the area that is closest to downtown. Using my park access analysis as an example, converting the final suitable polygons to points and running them through a cost distance tool would be one method to use.
However, I want to allow the citizens to provide input. In the next entry in this series, I’ll use ArcGIS Server to collect volunteered geographic information, crowd-sourced, or user-generated content to allow users to vote on their favorite location for a new park. This concept is now being referred to as “participatory planning”.
Accessing the data and models
The data and models for this blog post can be found here
The rest of the data and tools for this blog series can be found in the Park Analysis and Design group here (make sure to filter by Show: All Content at the top of the page)
Content for the post from Matthew Baker
Park analysis and design – Measuring access to parks (part 1)
Have you ever wondered how far you are from a park? In this post, I’ll examine the placement of parks in Redlands, California, and determine which areas are best and worst served by a park. In future posts, I’ll discuss siting a new park using binary suitability analysis, web-based tools for evaluating and increasing park access, and the design of a new park using ArcMap and feature template-based editing.
Over the last year, I’ve been attending various urban planning conferences and have discussed with several urban planners the need to design healthier communities, and I have heard this notion echoing throughout the planning community.
One concern is to figure out how well areas are served by parks. In my analysis, I want to determine which areas are within one mile of a park and visualize the results in a way that is easy to understand. I chose one mile, assuming most people can visualize how long it would take them to walk a mile, but this analysis could certainly be easily altered to measure any distance and present the results in a similar manner.
To do this, I could use a simple one-mile buffer around the parks, as the first map shows. However, a map created that way does not consider modes of travel. I want to measure pedestrian access to parks, so the best route is to travel along a road, preferably on the sidewalk.
The more accurate way to measure park access is to determine areas around the parks that fall within a specified distance from the parks along the road network. Using network analysis, we call this a service area analysis, or drive time, but this uses the road network only.
There are tools within the Spatial Analyst toolbox to run a cost-distance analysis: essentially a distance map calculated against a surface describing how difficult it is to travel across a landscape. This gives me the ability to rank our landscape by how easy it is to travel, road or not.
I want to then create a map showing areas that are ¼, ½, 1 mile, and greater than 1 mile from a park along the road network and show the distances on the map as well as on a graph.
Creating a travel cost surface
For my analysis, I am first going to create a cost surface that describes ease of travel through Redlands, with areas along roads being easier (cheaper) to travel through, and areas farther from roads more difficult (expensive) to travel.
To do this, I start by creating a raster surface where every cell has a value for the distance it is from itself to the nearest walkable road segment; that is, I don’t have to drive a car to get to a park and can even get exercise on the way.
First, I’ll need to map the road network. From the City of Redlands roads dataset, I can simplify all the roads into three main types: minor, major (arterial), and highway.
Since pedestrians cannot safely or legally walk on the highways, I can remove them from the analysis. The first tool in the model will be the Select tool, which allows a set of features to be removed for analysis by an SQL statement. In this case, I’ll use Road Type not equal to Highway to remove the highways from the analysis and create a walkable road dataset.
Of course, this would be a good place for a better road dataset in which each street had an attribute for whether or not it is walkable. I have heard of a few communities and organizations starting to capture this data, and it would be most useful for this application.
Once I have extracted the walkable roads, I’ll run the Euclidean Distance tool to create a surface in which each raster cell holds a value for the distance between itself and the nearest road.
The Euclidean Distance tool creates a surface where every part of the study area is broken down into a square (cell), and every square is assigned the distance to the nearest road segment. I’ve adjusted the symbology to group cells into distance bands.
Creating a cost surface
I’ll now borrow a concept from a weighted overlay (suitability) model and reclassify the road distances onto a scale of 1 to 6, where 1 is the cheapest (easiest to travel), and 6 is the most expensive (difficult to travel).To do this, use the Reclassify tool. It allows me to define the number of classes into which I want to reclassify the data. The Old Values column describes the distances from the Euclidean distance raster. The New Values column is the breakdown of the new values for the ranges of the old distance values.
Notice I’m going to reclassify the distances using the same distance bands I used earlier to describe how far each part of town is from the nearest road. Each cell in each distance band then gets a new value describing its cost on a scale of 1 to 6.
Here are the new reclassified distances. Notice the values become more expensive when moving away from the roads.
This now becomes the cost surface that I’ll use to measure park access.
Evaluating park data
Because the park data is stored as centroid points, they may not necessarily reflect the true access points to the parks themselves. By creating points at the corners of the park, I can have a more suitable location from which to measure park access.
Borrowing again from the City of Redlands dataset, I’ll simply select the parcels that intersect the park points and run those intersecting parcels through the Feature Vertices To Point tool in the Data Management toolbox.
Depending on the geometry of some of the parcels, I might end up with a little more than just the corners, but this is a much more accurate representation of how to get into the park than just a point in the middle of the parcel.
Calculating cost distance
Next, I’ll run the new park points against the cost surface using the Cost Distance tool in the Spatial Analyst toolbox. Using this tool, I can create a raster surface where each cell has a distance from itself to the nearest park point along the cheapest path—in this case, the cells that are nearest to the roads as described by our cost surface.
The resultant raster gives a picture of how far each location is in the entire city to the nearest park, which is somewhat hard to visualize. I can then reclassify the distances into simple ¼-, ½-, and 1-mile areas.
Visualizing the results
Taking the walkable road network into consideration certainly does give a much better picture of areas served by parks—and notice the areas that now show up as underserved that the buffer didn’t expose. These areas are over a mile from a park, which meets our criteria of underserved.
In addition to mapping, I can also create a graph that visualizes the percentages of the city that are served by parks by their respective distances.
Using the graphing tools in ArcMap, I can create a new field of data to hold the percentage, calculated by using a variable in the model that stored the area of the City, and divide that by the area of each feature in my walkability analysis. I can create a table that stores the values of the output of my reclassification (1,2,3,5,9) and their respective labels (500’, ¼ Mi, ½ Mi, 1 Mi, and More than 1 Mile) and join that table to my walkability output. It’s an extra step, but one that can be repeated if my underlying data changes and I want to run it again.
Now that I have identified that there are areas underserved by parks, the task of my next blog post will be to determine the best location for a new park using a simple binary suitability analysis.
Data is provided by the City of Redlands. The data and models for this blog post can be found here
Content for the post from Matthew Baker
(SP1) or prior cannot be opened or saved after installing Service Pack 2 (SP2).
ArcMap may also crash at Service Pack 2 when switching from the Data
View to the Layout View or when working with map surrounds such as Legend, North
Arrow, Scale Bar, and Scale Text.
functionality to save the map document to version 8.3, 9.0 or 9.1 and the map
document contains map surround elements.