Despite its singular name, it is in fact a collection of files – with a minimum of four key files: (.shp. The data is in Shapefile format which is the de facto standard for sharing map data or publishing your data to a web map or online GIS. Exporting the filtered data as a Shapefileįor those that don't have any data, but want to play along at home, we've prepared a sample Shapefile of US Counties for you to work wth. Creating a selection to delete information outside our area of interest 3. In this tutorial, we’ll cover the following: 1. Once selected, removing them is as simple as hitting the delete key. In QGIS, this expression would create a selection of all counties in the dataset, except for those with a STATE attribute value of Texas. Just like we could select a range in Excel with a simple =A1:A10, in a GIS we can create an expression to select a subset of features.įor example, we can isolate the unwanted areas in our US County Shapefile with a simple expression: An expression in GIS is much like a formula in Excel. After all, you found this tutorial, so you’re on third base and the home stretch is in sight. If you’ve found spatial data and are looking to filter out the unwanted data, I’m going to assume you know a little bit about mapping. Sounds like it’s going to be complicated, I know, but I’ll make this painless. “Features? Expressions? Queries?!! I just want to map my sales data!”

In a GIS this is done by selecting our desired features using an expression or query, and deleting the rest. The task here is to remove all of the features from the dataset that you don’t need. Short of making a strange map with lots of plain colored areas and then some nice shaded Texan counties, what can we do to trim the fat, so to speak, and filter out all the information we don’t need while keeping all the good data we do need? If you’ve ever downloaded a shapefile from the US Census Bureau’s website, you’ll find this is a common problem. Problem is, like most map data sourced from third parties, this Shapefile contains features and information outside of your area of interest - in fact, it contains geometry and attributes for every single US county. Now, you’re ready to make a web map of sales data for Texas or add the data to your online GIS. So you’ve sourced the perfect shapefile covering US Counties with demographic and population data, and some neat geographic information like the square mile area of land and water for each county.

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