One option would be the GEOnet Names Server published by the US National Geospatial-Intelligence Agency. It is a gazetteer of global place names that includes a variety of spellings in different languages, including the common English variants, plus longitude and latitude coordinates. It includes administrative divisions, cities and towns, concentrated ...
One possibility might be a Postgis server
Postgis is a Postgres extension that allows the storage and querying many types of GIS data including geojson. This would also allow you to store the data along with the timestamp for it's creation.
If you know the users who need to access the data you can create accounts for them and they can submit queries to ...
US census geography follows a strict hierarchy, and two features within the same type of geography are discrete and can never overlap and cover the same area (tracts can't overlap tracts, counties can't overlap counties, etc). In your example, tract 9502 is completely surrounded by tract 9501, or to put it another way, tract 9501 is like a donut with a hole ...
As Barry Carter explained, parcel data in the US is generally maintained at the county level. Unfortunately this means you usually have to download it from a separate source for each county. Here's a quick explanation of how to find parcel data downloads.
Usually the parcel data can be found by searching for the county auditor's website. Be sure to include ...
It's a big YMMV, but I wrote a scraper for Google Maps "Popular Times", both the hourly data for a normal week, as well as the current "live" value.
You can get PM10 and other air pollution measurement data from multiple locations in the city of Zürich, Switzerland
The data comes either as
hourly, for the last 24 hours, updated every hour
daily, for the last 30 days, updated every day
daily, going back to 2012 (and also 1983-2011), updated ...