cityofchicago/chicago-traffic-tracker-historical-congestion-sxs8-h27x
Icon for Socrata external plugin

Query the Data Delivery Network

Query the DDN

The easiest way to query any data on Splitgraph is via the "Data Delivery Network" (DDN). The DDN is a single endpoint that speaks the PostgreSQL wire protocol. Any Splitgraph user can connect to it at data.splitgraph.com:5432 and query any version of over 40,000 datasets that are hosted or proxied by Splitgraph.

For example, you can query the chicago_traffic_tracker_historical_congestion table in this repository, by referencing it like:

"cityofchicago/chicago-traffic-tracker-historical-congestion-sxs8-h27x:latest"."chicago_traffic_tracker_historical_congestion"

or in a full query, like:

SELECT
    ":id", -- Socrata column ID
    "start_latitude", -- Latitude of the start of the segment.
    "bus_count", -- Number of buses providing a GPS feed used to estimate congestion.
    "end_location", -- Location of the end of the segment.
    "month", -- Month of the year.
    "end_latitude", -- Latitude of the end of the segment.
    "length", -- Length of the segment in miles.
    "comments",
    "hour", -- Hour of the day.
    "time",
    "direction", -- Traffic flow direction for the segment.
    "record_id", -- A unique identifier for each record in the dataset.
    "street_heading", -- The position of the segment in the address grid. North, South, East, or West of State and Madison. 
    "from_street", -- Start street for the segment in the direction of traffic flow.
    ":@computed_region_43wa_7qmu",
    "to_street", -- End street for the segment in the direction of traffic flow.
    ":@computed_region_6mkv_f3dw",
    "start_location", -- Location of the start of the segment.
    "street", -- Street name of the traffic segment.
    "message_count", -- Number of GPS probes received(or used) for estimating the speed for that segment.
    ":@computed_region_vrxf_vc4k",
    "end_longitude", -- Longitude of the end of the segment.
    "day_of_week", -- Day of the week. Sunday = 1
    "segment_id", -- Unique arbitrary number to represent each segment.
    "start_longitude", -- Longitude of the start of the segment.
    "speed" -- Estimated traffic speed in miles per hour. A value of -1 means no estimate is available.
FROM
    "cityofchicago/chicago-traffic-tracker-historical-congestion-sxs8-h27x:latest"."chicago_traffic_tracker_historical_congestion"
LIMIT 100;

Connecting to the DDN is easy. All you need is an existing SQL client that can connect to Postgres. As long as you have a SQL client ready, you'll be able to query cityofchicago/chicago-traffic-tracker-historical-congestion-sxs8-h27x with SQL in under 60 seconds.

This repository is an "external" repository. That means it's hosted elsewhere, in this case at data.cityofchicago.org. When you querycityofchicago/chicago-traffic-tracker-historical-congestion-sxs8-h27x:latest on the DDN, we "mount" the repository using the socrata mount handler. The mount handler proxies your SQL query to the upstream data source, translating it from SQL to the relevant language (in this case SoQL).

We also cache query responses on the DDN, but we run the DDN on multiple nodes so a CACHE_HIT is only guaranteed for subsequent queries that land on the same node.

Query Your Local Engine

Install Splitgraph Locally
bash -c "$(curl -sL https://github.com/splitgraph/splitgraph/releases/latest/download/install.sh)"
 

Read the installation docs.

Splitgraph Cloud is built around Splitgraph Core (GitHub), which includes a local Splitgraph Engine packaged as a Docker image. Splitgraph Cloud is basically a scaled-up version of that local Engine. When you query the Data Delivery Network or the REST API, we mount the relevant datasets in an Engine on our servers and execute your query on it.

It's possible to run this engine locally. You'll need a Mac, Windows or Linux system to install sgr, and a Docker installation to run the engine. You don't need to know how to actually use Docker; sgrcan manage the image, container and volume for you.

There are a few ways to ingest data into the local engine.

For external repositories (like this repository), the Splitgraph Engine can "mount" upstream data sources by using sgr mount. This feature is built around Postgres Foreign Data Wrappers (FDW). You can write custom "mount handlers" for any upstream data source. For an example, we blogged about making a custom mount handler for HackerNews stories.

For hosted datasets, where the author has pushed Splitgraph Images to the repository, you can "clone" and/or "checkout" the data using sgr cloneand sgr checkout.

Mounting Data

This repository is an external repository. It's not hosted by Splitgraph. It is hosted by data.cityofchicago.org, and Splitgraph indexes it. This means it is not an actual Splitgraph image, so you cannot use sgr clone to get the data. Instead, you can use the socrata adapter with the sgr mount command. Then, if you want, you can import the data and turn it into a Splitgraph image that others can clone.

First, install Splitgraph if you haven't already.

Mount the table with sgr mount

sgr mount socrata \
  "cityofchicago/chicago-traffic-tracker-historical-congestion-sxs8-h27x" \
  --handler-options '{
    "domain": "data.cityofchicago.org",
    "tables": {
        "chicago_traffic_tracker_historical_congestion": "sxs8-h27x"
    }
}'

That's it! Now you can query the data in the mounted table like any other Postgres table.

Query the data with your existing tools

Once you've loaded the data into your local Splitgraph engine, you can query it with any of your existing tools. As far as they're concerned, cityofchicago/chicago-traffic-tracker-historical-congestion-sxs8-h27x is just another Postgres schema.