PLEASE interrupt if you have questions!

Go to http://lyzidiamond.com /geodata to follow along.

(Use left and right arrows to navigate. Links have a blue background.)

First things first: What is geographic data?

Geographic data represents things that have a location.

This can include physical things like roads, rivers, and cities.

It can also include ephemeral phenomena, like rainfall rates, 911 calls, and weather patterns.

Geographic data can also capture nuances of locations, like the degree of slope at a specific location on the side of a mountain.

How do we use geographic data?

Typically, geographic data is used for two things: visualization and analysis.

It is often used for both!

There are many different types of geographic data, used by many different types of software, web tools, and libraries, for many different use cases.

Fortunately, we have many resources at our disposal to transform data from one type to another.

Let's first talk about the types of geographic data and their use cases.

Geographic data typically falls into two camps: raster data and vector data.

I am most often working with vector data, so let's start there.

Vector geo data has three things: geometry, a location, and attribute information.

One super common geographic data format is the shapefile.

Shapefile is actually a misnomer: the data format requires three different files to store its core data (plus some optional files).

Let's take a look at a shapefile. Head over to http://bit.ly/orgeo and download the Cities shapefile.

Clicking the link should have downloaded cities.zip. Extract that to a folder and take a look at the files in it.

There are two files that are unrelated to the shapefile: the PDF file and the HTML file. We can ignore those for now.

There are four other files in the folder: a dbf, a prj, a shp, and a shx.

The three mandatory files are the dbf, the shp, and the shx.

Open up the dbf file in a text editor.

The dbf contains the attribute information for the dataset, with different values for each feature.

Now open up the prj file in a text editor.

The prj contains the projection information for the dataset.

(Projections deserve their own discussion. :-P)

We can skip the shx file. It is an index file to allow quick seeking within the file.

Ah, now to the shp file!

If you have QGIS or ArcGIS installed on your machine, open up the cities.shp file.

The shp file contains the dataset's geometry information. (Points, lines, polygons, etc).

Open the attribute table for cities.

Check out the properties of the cities file, and take a look at the projection (or coordinate reference system).

Shapefiles can be used with most desktop GIS and spatial analysis tools.

Shapefiles are not used in web maps.

Another extremely popular geographic data format is GeoJSON.

Let's look at some GeoJSON!

Head to http://bit.ly/maptimegj

GeoJSON is an extension of a format called JSON, which stands for JavaScript Object Notation.

Because GeoJSON is basically just JavaScript, it can easily be used in web maps!

GeoJSON has some required attributes. GeoJSON features need a type, geometry, and properties.

To learn more about GeoJSON's specificities, check out Learn GeoJSON. #shamelessplug

In a future Maptime exercise we will work on putting GeoJSON files on web maps. :)

Another format: KML.

KML stands for Keyhole Markup Language. It is a file format from Google for use in Google Earth and Google Maps.

KML stores data in a tag-based format. This is similar to GeoJSON, except GeoJSON uses key-value pairs instead.

Head over to http://bit.ly/basickml and play around with different types of KML files.

There are many many other types of geographic vector data, but one last one I'd like to mention here is none other than OpenStreetMap.

Head to http://osm.org and click Export at the top.

A file called map.osm should download. Open it in a text editor.

OSM data is sort of like KML, but has different information.

It contains a node id, changeset number, user, and of course latitude and longitude, among other info.

Let's quickly talk about raster data.

Like vector data, raster data contains location. But it stores its attribute information differently.

Raster data stores its information in its pixels. This information can include height, slope, direction, color, and many others.

As far as formats, a very popular one is the GeoTIFF.

OMG GeoTIFF

A GeoTIFF is simply a TIFF (tagged image file format) file that maintains location information.

The most typical uses for rasters in a geographic context are digital elevation models and aerial photography. These can be used to make other things, too.

Just as many spatial problems can be solved with raster data as vector data. What are some of them?

Homework:Check out OpenTopography at http://opentopography.org and take a look at some elevation data.

In addition to rasters and vectors, there's one other very popular geo data type.

Geographic data is very commonly stored in tables of various types.

These include CSV, Excel, Google Spreadsheets, and many others.

Tabular data can be geocoded to be displayed on a map.

(Geocoding also deserves its own conversation.)

There are many more formats than the ones we just talked about.

There's the file geodatabase, TopoJSON, PostGIS, SpatiaLite, Well-known Text, Web Feature Service, and even more.

(If you're going to poke around, check out PostGIS first. Super powerful.)

Much of the work in geo these days requires some data transformation.

There are many tools that allow for transformation, including QGIS, GDAL, and OGR2OGR, among others.

Geographic data exists in a variety of formats.

Shapefiles are commonly used for spatial analysis and visualization on your desktop.

GeoJSON and KML are commonly used for web maps.

You can download vector data from OpenStreetMap!

There are lots of places on the internet to find geographic data.

Heck yes!

Just knowing about these few data types can make you a very strong geographic data user.

YOU'RE A CHAMPION! Keep learning more!

Thanks.

Lyzi Diamond, @lyzidiamond, lyzidiamond.com