Geo-Information

E2: Symbolization in a GIS

Warm Up

Firstly, let’s talk about what symbolization actually means.
At its core, symbolization is about how we visually represent spatial data — turning raw points, lines, polygons, or rasters into something meaningful and readable on a map.

What is Symbolization?

Symbolization is the process of assigning visual variables (color, size, shape, pattern, transparency, etc.) to spatial features so they communicate information effectively.

For example:

🟢 Points: Size or color might indicate population of a city.
📏 Lines: Thickness might show traffic capacity; dashed lines could represent underground routes.
🗺️ Polygons: Fill color could show land use types; transparency could reveal imagery underneath.
🖼 Rasters: Color ramps might represent elevation or temperature.

Goal: Ensure that the symbol (what you draw) matches the referent (what it means in the real world) — clearly, consistently, and intuitively.

Cartographers have developed a set of visual variables (shape, size, orientation, color, pattern, transparency, etc.) to express these symbol–referent relationships. The choice of variable depends on whether your data is qualitative (categories) or quantitative (numbers).

Types of Symbolization in GIS

We’ll work with multiple styles today:

Uniform Symbolization – Same style for all features (e.g., all bus stops shown with the same icon).
Qualitative Symbolization – Different styles for different categories (e.g., different colors for museums vs. schools).
Quantitative Symbolization – Styles vary based on numeric values (e.g., darker shades for taller buildings).
Proportional & Graduated Symbols – Symbol sizes vary with data values.
Cased Line Features – Multi-layered lines to improve visual clarity.
Scale-based Symbolization – Symbols change visibility or size depending on zoom level.
Transparency – See layers underneath while still keeping context.

Task

Descriptions

Detailed instructions in {download}Lesson 2 <../doc/Lesson 2.docx>

& You can Click here to look

Data

Students.gdb
Project created in E1.

Overview

1. Uniform Symbolization – Bus Stops

Add bus_stops layer from Data Students.gdb.
Use Single Symbol style → choose an appropriate point symbol from the gallery.
Adjust fill color and size under Properties → Appearance.

2. Tram Stops & Underground Stations with External Symbols

Open Format Point Symbol → Properties → Layers.
Import Tram_logo.svg or UBahn_logo.svg from the Symbols folder.
Adjust symbol size if needed.

3. Qualitative Symbolization – Museums & TUM

Buildings layer → Symbolize by tourism field (Unique Values).
Make museums stand out with a unique color.
Add second field (amenity) to also show TUM buildings distinctly while keeping museums highlighted.

4. Quantitative Symbolization – Building Heights

Use Graduated Colors on building height (calculated via Arcade: $feature.level_num * 3.5).
Test different classification methods; create a separate class for “no data” (color it light grey).

5. Proportional Symbols – Roads by Speed

Proportional Symbols style → Field: speed_num.
Set minimum size = 0 to hide no data; choose an appropriate max size.

6. Cased Line Features

Unique Values → Field: type_of_road.
Select main road classes → apply cased road style.
Move symbol layers to join and merge intersections properly.

7. Scale-Based Symbolization

Roads:
- Main roads visible at 1:10,000 and larger.
- Minor roads visible at 1:5,000 and larger.
Public transport:
- Adjust size stops for different zoom levels (e.g., 50pt at 1:1,000 → 1pt at 1:100,000,000).

8. Transparency

Adjust building transparency so orthophoto shows through.
Try the swipe tool to compare layers interactively.

9. Combining Skills – Underground Lines

Create line_number field and populate values for U-Bahn lines.
Symbolize by category:
- Solid strokes for U1/U2.
- Bicolored dashed+solid for shared lines U3/U6 and U4/U5.
Sort underground lines under buildings to indicate they’re below ground.

Advance Task

Use Arcade expressions to create new fields dynamically.
Use online tools such as Maputnik to explore and experiment with additional map styles you like.