Category: Information

Don’t ban apartments on this vacant lot if you want more affordable housing – a case study

August 2, 2018 / / 0 Comments

A vacant lot is for sale near the 606’s Bloomingdale Trail, a popular amenity that’s now known to have an effect in increasing home values. It’s zoned RS-3, which means it bans apartments. If the zoning stays the same, then the vacant lot will only allow a rich family to move in here. If the lot’s zoning is changed to allow apartments or condos, then the vacant lot could welcome families that earn median incomes.

You can build multi-family housing on the lot if you can get a zoning change, but you’ll have to pay the city a fee, convince your future neighbors that they shouldn’t oppose it, convince the alder that he should support it, and you’ll have to hire a lawyer.

Let’s say that zoning changes in Chicago were free and frictionless*. What should be built on this lot?

If the lot would allow multi-family housing, we can build several units for less money per unit than if we built a single-family house. That means that three families (let’s stick with three, which requires a zoning change to RM-4.5) could be housed for less money per family than the cost of one family.

How’s that? The sticker price for this lot is $425,000 right now, and if one family is paying for that plus the cost of building a house, then your minimum investment is pretty massive. (I suspect the lot will sell for something closer to $400,000.)

I looked at new construction costs on Chicago Cityscape, as indicated on building permits issued within 1 mile of the vacant lot, took the average, and added it to the cost of land per unit.

Construction costs

The average new construction single-family house, from the 10 most recent permits, is $304,052.78.

The average new construction multi-family housing, from the 10 most recent permits, is $230,192.13 per unit.

Total cost per unit (land + construction)

Add in the land cost per unit ($425,000 for the single-family house and $141,666.67 per unit for the 3-flat) and you end up with the total costs of:

  • $729,052.78 for the single-family house
  • $371,858.80 per unit in the 3-flat

Add in the profit or “cap rate” that a builder wants to make and the price is even higher, but the people who would buy in the multi-family house would be paying much less for their homes.

Takeaways

The city can generate more affordable housing if it “upzones” vacant land and stops banning multi-family housing. (Much of the city’s parcels have been “downzoned” to ban multi-family housing in a process that creates “exclusionary zoning” and allows only – expensive – single-family housing.)

The city and the Chicago Transit Authority will earn more real estate transfer taxes (RPTT) from the sales of the units as condos than from a single-family house.

Three families instead of one would enjoy living to the wonderful amenity that the Bloomingdale Trail and the parks that the 606 offers.

Want this kind of analysis for a property in Chicago? You can order a zoning report from me.

* The City of Chicago charges a zoning change fee of $1,025, and you will most likely have to hire a lawyer, and it will take about 3-6 months, depending on the complexity of the proposal that requires the zoning change. You can use Chicago Cityscape to see actual approval times (excluding the time meeting the alder for the ward of the proposed project).

Is it possible for us to “greenline” neighborhoods?

May 24, 2018 / / 0 Comments

(I don’t mean extending the Green Line to its original terminal, to provide more transportation options in Woodlawn.)

Maps have been used to devalue neighborhoods and to excuse disinvestment. There should be maps, and narratives, to “greenline” – raise up – Chicago neighborhoods.

The Home Owners’ Loan Corporation “residential lending security” maps marked areas based on prejudicial characteristics and some objective traits of neighborhoods to assess the home mortgage lending risk. (View the Cook County maps.) The red and yellow areas have suffered almost continuously since the 1930s, and it could be based on the marking of these neighborhoods as red or yellow (there is some debate about the maps’ real effects).

The Home Owners’ Loan Corporation and its local consultants (brokers and appraisers, mostly) outlined areas and labeled them according to objective and subjective & prejudicial criteria in the 1930s. Each area is accompanied by a data sheet and narrative description. The image is a screenshot of the maps as hosted and presented on Chicago Cityscape.

The idea of “greenlining”

I might be thinking myopically, but what would happen if we marked *every* neighborhood in green, and talked about their strengths, and any historical and current disinvestment – actions that contribute to people’s distressed conditions today?

One aspect of this is a form of affirmative marketing – advertising yourself, telling your own story, in a more positive way than others have heard about you in the past.

In 1940, one area on the Far West Side of Chicago, in the Austin community area, was described as “Definitely Declining”, a “C” grade, like this:

This area is bounded on the north by Lake St., on the south by Columbus Park, and on the west by the neighboring village of Oak Park. The terrain is flat and the area is about 100% built up. There is heavy traffic along Lake St., Washington Blvd. Madison St., Austin Ave. (the western boundary) and Central Ave. (the eastern boundary).

High schools, grammar schools, and churches are convenient. Residents shop at fine shopping center in Oak Park. There are also numerouss small stores along Lake St., and along Madison St. There are many large apartment buildings along the boulevards above mentioned, and these are largely occupied by Hebrew tenants. As a whole the area would probably be 20-25% Jewish.

Some of this migration is coming from Lawndale and from the southwest side of Chicago. Land values are quite high due to the fact that the area is zoned for apartment buildings. This penalizes single family occupancy because of high taxes based on exclusive land values, which are from $60-80 a front foot, altho one authority estimates them at $100 a front foot. An example of this is shown where HOLC had a house on Mason St. exposed for sale over a (over) period of two years at prices beginning at $6,000 and going down to $4,500. it was finally sold for $3,800. The land alone is taxed based on a valuation exceeding that amount. This area is favored by good transportation and by proximity to a good Catholic Church and parochial school.

There are a few scattered two flats in which units rent for about $55. Columbus Park on the south affords exceptional recreational advantages. The Hawthorne Building & Loan, Bell Savings Building & Loan, and Prairie State Bank have loaned in this area, without the FHA insurance provision. The amounts are stated to be up to 50% and in some cases 60%, of current appraisals.

Age, slow infiltration, and rather indifferent maintenance have been considered in grading this area “C”.

Infiltration is a coded reference to people of color, and Jews.

My questions about how to “greenline” a neighborhood

  1. How would you describe this part of Austin today to stand up for the neighborhood and its residents, the actions taken against them over decades, and work to repair these?
  2. How do you change the mindset of investors (both small and large, local and far) to see the advantages in every neighborhood rather than rely on money metrics?
  3. What other kinds of data can investors use in their pro formas to find the positive outlook?
  4. What would these areas look like today if they received the same level of investment (per square mile, per student, per resident, per road mile) as green and blue areas? How great was the level of disinvestment from 1940-2018?

In the midst of writing this, Paola Aguirre pointed me to another kind of greenlining that’s been proposed in St. Louis. A new anti-segregation report from For the Sake of All recommended a “Greenlining Fund” that would pay to cover the gap between what the bank is appraising a house for and what the sales price is for a house, so that more renters and Black families can buy a house in their neighborhoods.

That “greenlining” is a more direct response to the outcome of redlining: It was harder to get a mortgage in a red area. My idea of greenlining is to come up with ways to say to convince people who have a hard time believing there are qualities worth investing in that there they are people and places worth investing in.

The Digital Scholarship Lab at the University of Richmond digitized the HOLC maps and published them on their Mapping Inequality website as well as provided the GIS data under a Creative Commons license.

The genius of using ST_Subdivide to speed up PostGIS intersection comparisons

December 14, 2017 / / 0 Comments
You should use ST_Subdivide to break up large shapes into smaller ones

This infographic visually compares the difference between running a PostGIS comparison query like ST_Intersects on a large shape versus a subdivided version of that large shape. Click to embiggen.

Hundreds of GIS intersection comparisons are completed every hour on Chicago Cityscape.*

People are looking at, say, a map of the South Shore community area. That “Place” page then grabs all of the building permits, building violations, business licenses, and other “feature layers” that are stored as points.

A classic “point in polygon” comparison is made using the ST_Intersects(place_geometry, permits_geometry) function.

This has worked very well for several years.

The problem

But as Chicago Cityscape handles larger shapes – they come from users drawing their own, large shapes, and from large shapes like the downtown Chicago area – this query doesn’t cut it.

Setting indexes on the geometry is imperative, but it’s not the end of the to optimize performance. That’s because the index of the geometry is a rectangular bounding box (which is also called an “envelope” in GIS) that contains the entire shape of the South Shore community area.

The downtown Chicago area, however, is not even the largest shape I have. That belongs to the new Place, “Neighborhood Opportunity Fund investment zones” (NOF). Combined, they cover 75 square miles of Chicago. Downtown is only 7.7 square miles.

After I added the NOF map and tested its Place page, it “crashed” my server, metaphorically speaking. The query to just count the number of building permits in the area would take about five minutes.

There had to be a better way; in the meantime, however, I divided the NOF map into the West and South sections. This hardly improved the counting time.

The solution

Thankfully, today, I saw a tweet from Paul Ramsey linking to his blog that linked to his slides from a recent presentation about the use of PostgreSQL to store and manipulate GIS data.

In it he explained how the ST_Subdividefunction worked. I’m going to demonstrate it using graphics from my own maps.

A normal intersection comparison, using ST_Intersects(place_geometry, permits_geometry) in a query creates a bounding box (envelope) around each geometry and quickly determines whether the two envelopes overlap. If they do, then it checks again to see if the actual geometries overlap. If they do, that data is returned as a response to your query.

When your two datasets are massive, like the NOF zones, which collectively cover 1/3rd of Chicago, and the building permits, which are found across the entire city…well, that led to the five minutes counting time.

Enter ST_Subdivide. To use it properly you would run it against your existing geometry and store the much smaller shapes, derived from the big shape, in a new table. I applied the function to all the 22,203 maps that Chicago Cityscape has and stored their unique IDs and subdivided geometries in a new “lookup” table.

Now, any time I want to compare the building permits against the NOF, the building permits are instead compared to the small shapes that were subdivided.

The query

Chicago Cityscape uses a single table (created as a materialized view) to combine all 22,203 maps. Each map is stored in a source table (for example, there’s a table to hold the 77 community areas) and the materialized view runs once a day to combine all of the maps in the source tables. This ensures our data is managed well: different source tables can hold different information, and the single table holds only the name, type, and geometry of the source tables, for faster comparison. Each entry in the single table also has a “slug”, its unique identifier.

Thus, the materialized view of the subdivided maps is created from the aforementioned single table, using this query:

create materialized view view_places_subdivided as
select gid || '_' || random() as gid, slug, st_subdivide(geom) as geom
from view_places;

The “gid” is designed to create a new unique ID field, as the slug field will be repeated for every subdivided of each map. A unique ID field is necessary if you want to refresh the materialized view concurrently (to allow for other queries to access the materialized view while it’s being refreshed).

* The results are cached for a few hours, because the feature layers change 1-2 times per day and at different times each day, so the limited duration cache accommodates that. Ideally I would code a way to invalidate the cache when the feature layer data is updated.

Update 12/31/19: ST_Subdivide will fail if your geometries have any or certain geometry errors (I don’t know if it’s any kind of error, or certain kinds of errors that make the function fail). Chicago Cityscape has over 37,000 features that ST_Subdivide is attempting to process, and there is a lot of room for error in managing that many features from dozens of sources.

Upzone the 606

December 8, 2017 / / 3 Comments
Map of the single family-only zoning around the Bloomingdale Trail

The area in green only allows single-family houses to be built.

Something’s gotta give.

This is all of the land area within two blocks of the Bloomingdale Trail that allows only single-family housing to be built (view full map). This isn’t to say that multi-family housing doesn’t exist here; it definitely does, and there’s probably a handful of two-flats on a majority of the blogs.

All of the five parks of the 606 are within this two block radius, and 49.6 percent of the land allows only single-family housing to be built.

But why build a transportation corridor, a park, a new, expensive, public amenity, and not change the kind of housing – which often determines the kind of family and makeup of a household – that can afford to buy a home near here.

It’s already been shown that detached single-family housing prices have grown intensely the closer you get to the trail. That price growth has meant displacement for some, and “no chance to buy or build a house here” for many others.

There are still plenty of vacant lots within the mapped area; lots that should have a 2-4 unit building built on them, but where only a 1-unit building is allowed.

This map was made possible by the new Zoning Assessment tool on Chicago Cityscape. Read about it or use it now.

How much of the land within walking distance of a CTA station is zoned to allow multi-family housing?

November 17, 2017 / / 0 Comments

I recently created the Zoning Assessment tool on Chicago Cityscape, which shows a map of aggregated zoning districts in a given community area, ward, or near a CTA or Metra station. Per Paul Angelone’s suggestion, you can now show the walk shed – the area within walking distance to the station, following the streets.

The maps in this post show where one can build apartments (including a simple and common two-flat) within a 15 minute walk to the Logan Square Blue Line station, which has 24-hour service. Try it yourself.

Thirty-one percent of the walk shed allows multi-family housing.

In a second version of the same map, I’ve marked in red the gaps in the zoning map. These are areas that are zoned to allow only single-family housing. That doesn’t make sense: The land near rapid transit stations should be much denser than the land away from the stations.

Sixty-four percent of the walk shed allows only single-family housing. The remaining five percent are planned developments (at least the Mega Mall is going to have a couple hundred dwelling units), manufacturing, and parks.

And if most of the block is already zoned to allow multi-family housing, why are these parcels skipped?

This is the same map as the one above, but with areas that allow only single-family housing marked in red (however, I skipped some areas to save myself time).

How it works
The walk shed boundaries are generated by Mapzen’s isochrone service. The Zoning Assessment map asks Mapzen for the polygon of a specified walk shed (walk or bike, 10 or 15 minutes), receives the polygon and sends that polygon to a custom API on the Cityscape server, which compares that to the server’s copy of Chicago’s latest zoning map. The comparison is then returned to the browser and replaces the default Zoning Assessment map.