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Searching the web for authoritative data

With GIS being more accessible, and with more demand for GIS data, it truly is a good time for the GIS professional. However, you must be wary of datasets—How they were created? If they are maintained? And/or whether the data is complete or not? Inspect every dataset to find:

Metadata, if available
Who created the data?
Do field names make sense, or do you need a key/lookup table for them?
What scale was the data drawn at?
What is the accuracy, spatially and mathematically?
What is the licensing of the data?

These are some of the questions you should ask yourself when searching out data online.

Not all of your data needs are going to be useful as static files on your file server or local machine. It may be that the data you need is too large or changes so often you'd rather not have to go out every day/week/month to download the newest version. There is a lot of dynamic data being served out in the web, so when you access it, you are always getting the most up-to-date data and only getting the data you need. Not having to store the data locally and being able to just pull the data from a server can be very advantageous. For example, if you want to create a map showing the current weather, it may not be necessary to keep the weather data for a historical archive. The purpose of the map is to show current weather, so you pull live data from a governmental body or commercial provider to overlay your map. That way, if it's a web map, you don't have to worry about keeping things up to date, and if it's a layer in a static map, every time you export or print it will show the updated data. This works well when GIS is needed in an operations center where a large map is printed every so often.

Some of the biggest GIS data creators are governments. Many governments produce a whole lot of data, but most have one flaw. They don't advertise it well. Thankfully, search engine crawlers do a great job of digging deep into complex government websites and allowing us to search for the keywords we are looking for. Adding keywords like shapefile, geodatabase, GIS, REST, WMS, and WFS to what you are trying to find can make searching quicker. In the United States, you can use https://data.gov to search against a large amount of federal, state, county, and local data. In Europe, you have https://data.europa.eu or https://www.europeandataportal.eu.