Digitization
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Analog spatial information or non-digital geographic data is transformed into digital form through the process of digitization. Spatial data on maps or photographs are traced as points, polylines, or polygons during this process. It can be used in GIS for various purposes, including storing data, creating map layers, and capturing and displaying geographic information. Data that may be represented as numbers or symbols, such as text or graphics, typically makes up digital datasets. Analogue to digital image conversion is another option for the procedure. The term "GIS" refers to a type of software application that models various aspects of geography, including earth surfaces, scientific domains, and social-cultural phenomena. With numerous other software programme like CAD (Computer-Aided Design), 3D modelling, etc., digitization in GIS can be integrated. Digitization is crucial in a world increasingly shaped by rapid technological advancement. In line with these developments, the utility of GIS is increasing and has become a vital part of our daily life. Data digitization is critical for GIS specialists who must turn digital data into geographic data in order to work with it. As institutions modernize, digital systems ideally enhance efficiency, accessibility, and transparency. The explosion of big data enables deeper insights, driving innovation and informed decision-making. AI technologies thrive on digital infrastructure, transforming industries from healthcare to finance. Without digitization, societies risk falling behind in an era defined by digital progress. The gap between our analogue past and an increasingly digital future is thus partly bridged by digitization, yet we also have to acknowledge that this process poses many challenges.
Contents
Types of Digitization[edit]
Here are two fundamental ways of digitizing:
1. Manual Digitization
Manual digitizing is the process of manually copying an image by hand to create a digital file. A Puck, which is similar to a mouse, is used for hand digitizing. It is done with the use of digitizing tablets and has a high accuracy when compared to other digitizing procedures.
2. Automatic Digitization:
The process of transforming raster to vector data or 2D or 3D objects to digital data is known as automatic digitizing. The major goal of automatic digitizing is to improve the speed and efficiency with which GIS data is collected. This method allows for the effective collection, organization, and management of massive amounts of data. The fundamental purpose of automatic digitizers is to deliver real-time spatial data.
How to digitize[edit]
To digitize a file, there are four major steps, 1). importing image and georefencing 2). Selecting the type of feature class, 3). Marking the points to digitize on the data, 4). saving and exporting the data. The detailed tutorial is given below.
Major errors in Digitization[edit]
Digitization is a highly complex, yet useful process which is widely used in GIS. Often, the process entails several errors. These errors are a frequent problem when the digitizer translates the data in a map form from the image. Some major and common errors are: 1. Geodetic errors when there are discrepancies in the spatial dataset and coordinates do not match with the actual location of the object on earth.
2. Dangling nodes where the ends of a polygon during digitization do not match keep ‘dangling’ at the end.
3. Knots or loops, when there are extra vertices in the polyline or polygon and then leads to formation of a know or loop in the digitized map.
4. Overshoot or undershoot happens when the line digitized does not connect to the next line. If the line falls short, it is called undershoot. But if the line is too far away from the feature being digitized it is called an overshoot.
5. Silver polygon is when there is an empty, non-digitized polygon in-between multiple polygon.
Tutorial for digitization[edit]
Pre-processing[edit]
This section includes importing the image and georeferencing it to the desired CRS. The tutorial for this is in the section ‘Georeferencing’.
Adding Features: Point, Line and Polygon[edit]
Now, we will show you how to manually add features to a map or digitize features on map. This can be useful if you have a picture or a map of a location but need to highlight certain aspects. Another application is if you don’t have vector file for a imagery map, we can digitize the georeferenced map from the image. First, we will add some points to our map. Please open the Open Street Map and go to Leuphana Campus. We want to highlight some of the places where you can get coffee. First, we need to create a new layer. Go to Layer → Create New Layer → New Shapefile Layer
1) Give a name to the new layer. I called it “Where to get coffee.”
2) Choose the geometry type. This is “Point” for now.
3) Check whether you have the right coordinate system. We used EPSG: 4326 - WSG 84 so far.
4) New Field: It is required that you assign at least one variable to the objects of this layer. I call it “Coffee?”. Here, we can later fill in the name of the coffee places we highlight on the map. The type is “Text”, because we want to fill in text data, but it could be something else, depending on which value you want to assign to your point data. Click “Add to Fields List”.
5) Hit “OK”.
We start with adding points to the map manually.
1) Click on the pencil symbol (“Toggle Editing”) in the toolbar at the top (1.).
2) Click on the “Add Point Feature” which is right to the pencil (2.).
3) Now you can click on all the positions at the map, where you suspect there could be coffee.
4) Each time you add a point, you fill in the name of the place (Mensa, Plan B…) under “Coffee?” and add an ID number (1, 2, 3…).
5) Please note that you need to switch back to the hand symbol (called “Pan Map”) if you want to alter the position of the map section.
6) Don’t forget to save your changes by clicking on the “save” symbol right next to the pencil (3.).
Next, let’s try to add a line to the map.
1) Repeat the steps to create a new shapefile layer. Call it “How to get from library to cafeteria” and select “LineString” instead of “Point”.
2) Create one field that is called “Name” of the type “Text”. Don’t forget to press “Add to Fields List”.
3) Press “OK”.
Now you can add the line. Draw your favourite route from the library to the cafeteria. Yes, it’s exams phase and we are all hungry.
1) Make sure you have selected the right layer.
2) Select the pencil symbol.
3) Select the “Add Line Feature” right to the pencil (4.).
4) You can now add a line by clicking on the map. Each click is another junction. To end the line, you need to right-click.
5) Fill in the sections for ID and give your route a name.
6) As before, if you need to change the visible map section, switch to the hand-symbol and then go back to the “Add Line Feature” symbol.
7) Don’t forget to save your changes by clicking on the “save” symbol right next to the pencil (5.).
8) In case you misplaced a dot, just continue until the end. Then, chose the “Vertex tool” with which you can change the location of previously set points (6.).
Now you have created a line, well done!
Lastly, let’s draw a polygon which imitates the floor area of the Libeskind building.
1) Repeat the steps to create a new shapefile layer. Call it “Most unusual building” and select “Polygon”.
2) Create one field that is called “Name” of the type “Text”. Don’t forget to press “Add to Fields List”.
3) Press “OK”
Now you can draw the shape of the central building.
1) Make sure you have selected the right layer.
2) Select the pencil symbol.
3) Select the “Add Polygon Feature” right to the pencil (7.).
4) You can now add a polygon by clicking on the map. Each click is another junction. To end the polygon, you need to right-click.
5) Fill in the sections for ID and give your route a name.
6) As before, if you need to change the visible map section, switch to the hand-symbol and then go back to the “Add Line Feature” symbol.
7) Don’t forget to save your changes by clicking on the “save” symbol right next to the pencil (8.).
8) In case you misplaced a dot, just continue until the end. Then, chose the “Vertex tool” with which you can change the location of previously set points (9.).
Manipulating Polygons[edit]
We would like to show one more useful editing tool for vector shapefiles. Consider you want to digitize some polygons which directly neighbor each other. This is often the case for country borders. To save time and achieve a precise result, you can use the functions snapping and tracing. For training purposes, let’s imagine there will be an annex building next to the central building to create additional space for studying. When we draw the floor area of this new building, it needs to match the borders of the original central building exactly. Right-click at some empty space at the tool bar at the top to open the panel menu. Click on “Snapping Toolbar”. An additional toolbar will appear.
Select both “Enable Snapping” at the left (the magnet symbol (10.)) and “Enable Tracing” at the right of it (the lightning symbol (11.)). Select now the pencil and the “Add Polygon Features” again. Now you can add a polygon which neatly fits to the already existing shape of the original central building (shown in figure (a-g) below).
If you want to start anew, just hit ESC. If you want to finish right-click and save your new polygon. If you want to manipulate the polygon shapes even further, by moving them around, rotating them or cutting certain pieces, you can activate the “Advanced Digitizing Toolbar”. Right-Click on the toolbar at the top and select the “Advanced Digitizing Toolbar”.
The following tools will appear:
Visual Settings and Export of Maps[edit]
This now looks all very nice. But we’d like to make it even nicer by changing some colours and adding some name tags. To do so, we select the layer where we want to make visual changes and open the “Layer Styling Panel” (12.). It will appear at the right side, where you usually find the toolbox.
Under “Symbology”, you can for instance change the colour and opacity of your objects.
Under “Labels”, you can adjust the font type, size, colour etc. of any label you would like to assign to your object. Remember that you gave each point, line and polygon a name? Under “Value”, you can now chose the relevant property (I called it “Name”) and QGIS will display the name of each object automatically.
My resulting map looks like this (I removed the annex building to the central building; let’s be honest, it wasn’t such a great idea in the first place):
Finally, we can export our map and add some features like a title, a legend and a grid. Click on the “New Print Layout” symbol in the toolbar at the top left (13.) and enter a name for the map you’d like to export. I’ll call it “Leuphana Campus”. Now, the Layout window opens.
Click on the “Add Map” symbol at the left (14.).
Now you can drag a rectangle on the canvas. All the layers that are currently visible in the main window will appear in this rectangle.
To drag around the map until it is placed on the canvas as you want it to, you can use the “Select/Move Item” function (15.). You can also move the map content, i.e., select which part of the map is shown on the canvas using this tool (16.).
You find both in the left toolbar at the top.
You can add a title by using the “Add Label” tool (17.). I adjusted the position of the map to leave some white space for the title, but that’s up to you. You can change the properties of the title in the right panel under “Item Properties”.
To add a legend, click “Add Legend” in the toolbar at the left (18.). As before, you can draw a rectangle on the canvas and the legend will appear in this rectangle. QGIS automatically displays all layers in the legend but you can select only those that you want to be visible on the final map. As before, you can change the visual appearance of the legend (font type etc.) under “Item Properties” in the right panel.
Similarly, you can add other features such as a north arrow (19.) and a scale bar (20.) using the respective tools in the left toolbar. Lastly, you can export your map in various formats, for instance as a PNG File. Go to Layout → Export as Image and save your file.
Amazing!
Tutorial[edit]
When scanning a map to convert it into vector data:
Step 1: Import the scanned map
- Open a new QGIS project.
- Click Add Layer → Raster Layer.
- Add your scanned map (in image format, e.g., .tif, .jpg., .png).
- Note: You will get a warning message because there are no coordinates assigned and it will not be displayed. We will fix this in step 3.
Step 2: Convert to a suitable format (optional)
- If your scan is not in .tif format, consider converting it fot better compatibility with georeferencing tools.
- Go to Raster → Conversion → Translate.
- Choose the layer you want to convert and where to save the new file. You can change the format of the output to .tif when saving the file. Then click Run.
Step 3: Georeferencing
- Align the map to real-world coordinates using ground control points (GCPs).
- Use the Georeferencer tool under Raster.
- A detailed tutorial can be found under Georeferencing.
The authors of this entry are Neha Chauhan and Christoph Schwenck. Hannah Metke, Carlo Krügermeier and Ben Richter wrote the tutorials.