Spatial data adds a geographic dimension to a qualitative and/or quantitative data set, situating it in a particular location within a coordinate system relative to other data points. (The coordinate system can be a real-world system or a locally created one used to meet the needs of a particular project.)

Spatial datasets, in general, come in two distinct forms, vector data (points, lines, and polygons) and raster (or pixel data). Raster and vector data can come together in the creation of a wide variety of mapping projects, from a traditional figure with an explanatory legend and caption, such as might appear in an academic text, to an online interactive platform that allows for the searching or filtering of thousands of pieces of spatial data or hundreds of historical maps.

Vector Data

Vector data includes points, lines, or polygons (shapes made up of straight lines) containing spatial information that represent some sort of feature or event in a physical or imagined landscape and may contain other types of qualitative or quantitative information, called attributes. A point may represent a tree, a city, or a moment in time. Lines might indicate the street grid of a town, the path someone traveled across the world, or a social link between two communities. Polygons can mark the boundaries of a country or voting district, the catchment area of a river, or a single city block.

For example, the relatively simple and ongoing project from the Burn's Library collection pictured below uses vector point data to offer a selection of images and accounts from individuals and their observations about how the cities and landscapes they visited appeared. Users can filter the point data by data or search for particular location names in the search bar.

Raster Data

Raster consists of "cells" of data covering a specific area (its extent), with attribute values in each cell representing a particular characteristic. It may still consist of points, lines, and polygons, but these shapes are themselves composed of pixels (the way a jpeg or other image file type is).

Data of this type may take many forms, such as satellite imagery containing vegetation or elevation data, precipitation maps, or even an historical map, which has been given a spatial reference. Unlike vector data, raster data has a particular resolution, meaning each pixel represents a particular geographic region of a specific size.

Most projects combine various forms of vector and raster datasets.

An opportunity to explore one of the spatial databases discussed in the presentation to look more closely at how their data is organized and to create your own simple spatial dataset.

Create a few spatial points of interest using the format we saw above ObjectID, X (long), Y(lat), or any other attributes you want using GoogleSheets/Excel/OpenOffice; or explore one of the databases above and practice downloading and opening the datasets to get comfortable dealing with vector datasets.

Remember to save your file as a .csv when you are done!

Some Boston Spatial Databases:

Possible Datasets

Possibly useful datasets for exploring questions about segregation and redlining.

• (download CSV)

• (download Shapefile)

Bonus

Want to check your csv data real quick? Go to , create a New Map, and click "Import" to import your CSV data to make sure it's looking good. Otherwise, we will be checking it later when we get to ArcGIS online!

Map Warper is an open source map warper/map georectifier, and image georeferencer tool developed, hosted, and maintained by Tim Waters.

Creating an Account

In Map Warper, it is possible to browse and download maps others have uploaded into Map Warper without an account. To georectify your own map, however, you must make one. This also allows you to easily return to your maps later.

1. On the top right corner of the page, click "Create Account"

2. Select a username and password and enter an active email address.

3. Click "Sign up"! You should quickly receive an email to confirm your account

Upload a Map with any Available Metadata

Now that you are logged in, you can upload your own images to the Map Warper server in order to georeference them.

1. Clicking “Upload Map” on the main toolbar (note if you are not yet logged in, it will ask you to do so at this point)

2. Insert any available metadata and a description of the map. This is useful both for your own records and for anyone else searching for similar maps on the Map Warper server.

3. At the bottom of the page, choose to Upload an Image File from your local computer or from a URL. Once the file has been selected, click "Create"

Once the upload is complete, a new page will appear informing you that the map was successfully created as well as providing an image of the uploaded map.

Rectify a Map with Control Points

Now the map is on the platform, but it does not yet have any spatial information associated with it. The next step is to use what are called "control points" to place your map in a “real-world” coordinate system where it can interact with other types of spatial data.

Understanding the Georectifying Window

1. Once your image is displayed, select "Rectify" on the main toolbar.

2. This opens up the Georectifying page, the most important page in this tutorial. It is composed of two windows, one showing your map and one showing a “basemap” which you will be using to geolocate your map.

3. In the top right corner of each map there are a series of buttons that help you navigate the map and add control points

Add a control point to the maps

Move a control point that has already been added to the map

Pan around the map

The last two icons appear only on the basemap and are used to adjust it as needed to help with georeferencing

Change the basemap to a Custom, already georectified basemap of your choosing (if available)

Swap between the initial basemap and satellite imagery, depending on which is easier to georeference your map

Creating Control Points on your maps

1. Navigate on your map to an easily identifiable location. In this example, I have chosen the tip of the island in the middle of Paris that the Notre Dame Cathedral is on. Note that an external mouse with a scroll wheel can make the zooming/moving process easier; zoom and pan buttons are also provided in each window.

2. Click the “Add Control Point” icon, then click again on your map in the desired location. A little control point should pop up!

3. Swap to the basemap and click the “Pan” tool (the hand) to find the proper location, then again select the “Add Control Point” tool and click on the corresponding point on the Basemap.

Check for Error and Warp the Map

1. After you add the 4th control point, your table of points will start including error information, as the points are triangulated against one another. Note that this error may not mean that you are doing anything wrong, particularly in an older map that is not as spatially accurate as something more modern! On the other hand, if your error is quite high and you believe your map is relatively accurate, you may have misplaced a control point somewhere. Usually, high error is caused by a single point being misreferenced.

2. When you feel like you have enough points scattered around your map, we are ready to georectify the map! Remember you can always come back later and add new points or remove old ones if you feel like the result is not to your liking. To georectify your map, just click “Warp Image!” at the bottom of the page and you’ll get a notice that your rectifier is working.

When the map is finished rectifying, you will get a notification that rectification is complete. Now, you should be able to see your map overlaid on the Basemap, as well as be able to turn it on and off or more or less opaque to check for accuracy!

Exporting your Map

If the map is to your liking, you are ready to export. Map Warper offers a variety of ways to export your map depending on your needs

1. To export your map, Select the Export tab on the toolbar. A window like that seen below will pop up, giving you a variety of choices for exporting

Some exporting options:

• GeoTiff:

  • public domain standard; easily imported into a wide variety of spatial platforms like ArcGIS or QGIS; good for backing up your georeferenced map on your local computer or in cloud storage like Google Drive

• .kml:

Initially, QGIS only has a single basemap to work with, let's add it!

In your browser pane, find XYZ Tiles and click the down arrow to find the Open Street Map basemap. Click and drag it into your layers box, and it will appear on the map.

There are lots of different options for loading basemaps, but first you have to connect them to your project from their hosted locations online (or self host). Here's a fast way to get a bunch of standard basemaps though, thanks to Klas Karlsson (one of the main qgis devs)!

1) Download the python script below and open it in a text editor (e.g. notepad).

Ok, we've got a background map, now what about vector data?

Adding Premade Vector Data

Adding vector data depends on what kind of format your data is in. Let's run through the standard three types.

Styling your data

Let's look at different ways to style your data using some archaeological data from the site of Gabii originally imported as a .geojson.

When initially imported, all the polygons are red with a black outline, which gives us some general information about the location but doesn't really differentiate the different kinds of archaeological features present. To do that, we need to change our styling.

To get to the styling options (also called Symbology), just double click the layer name in your Layers pane.

Here you can select how you want your features to be styled; the default is "Single Symbol" but often times you will want Categorized, or for quantitative attibutes, Graduated, ways of displaying your features. For now, let's select Categorized.

When stylizing by category, you can select which Attribute(s) you want to stylize by; I'm going to select the Descriptio(n) field because that's the different types of features in my layer.

Once you've picked your attribute, clicking "Classify" at the bottom of the box will assign an initial style to each of your features.

Each feature type is now a different color! You could further customize each individual style if you wanted on the symbology page.

Or, here I have made the color of the outline of the feature change, rather than the fill, in order to make the map more understandable.

Lots can be done with symbology; feel free to explore!

Preparing to Export Your Figure

Exporting your figure to share with others or for publication is often the final product for your QGIS map. Here we talk about the basics.

So far we have been working in what I call "Data View" where you can create, edit, and generally mess with your data. Now we are going to look at Print Layout, which allows you to organize your map for publication.

To access print layout, go to Project-->New Print Layout. A box will appear asking for you to name the layout (useful if you are creating mulitiple figures, for example).

A new window will appear that lets you create your layout, almost like working in a word document.

The left toolbar is your friend, allowing you to add map windows to the figure, as well as things like maps, north arrows, titles, legends, and other labels.

Each time you add a feature, it will appear in what is basically the "Layers" sidebar of your print layout, allowing you to further edit its properties. Above I've quickly added a scale bar, north arrow, and legend to the map.

When it looks good, you can export the figure! My figure below is a .tiff

This portion of the incubator is focused on an introduction to spatial data (vector and raster), with workshops on creating spatial data and finding and georeferencing historical maps. Finally, the different datasets are combined in an ArcGIS online map.

1. An Introduction to Mapping, GIS, and Vector Data

2. An Introduction to Raster Data and Georeferencing Historical Maps

Bonus: QGIS Workshop (in progress)

QGIS (and its assoicate ArcGIS Pro/Desktop) are powerful tools used for a wide variety of purposes across many fields. And GIS in general is a huge subject, with entire degrees/certificate programs devoted to it. As such, we will barely scratch the surface in this workshop, but by the end you will be able to:

1. Understand a bit about the QGIS interface;

2. Search for and add pre-created basemaps;

3. Add your own georeferenced raster data;

4. Import basic vector datasets from csvs, shapefiles, and geojsons;

5. Create a new vector dataset from scratch;

6. Perform some basic styling of data;

7. Prepare your data for export.

That's a lot....lets get started!

For those interested in diving deeper, I highly reccomend reading the thorough ; much of the below is taken from there and the step-by-step Links to specific parts of the handbook are referenced above.

Explore one of the databases discussed in the presentation and download an historical map of interest (or use one of your own if you already have one!). Then, using the MapWarper online tool, georeference your map with at least 4 points.

Possible Mapping Geodatabases

• David Rumsey Map Collection ()

• Library of Congress Map Collection ()

• USGS Historical Topographic Map Explorer ()

Redlining Map Option

• To look at your data against an historical Boston redlining map, we recommend using one of the from the Boston Public library.

Georeferenced version of the redlining map: