What is Shadow Analysis?

Definition, uses, and tools for analyzing how shadows change throughout the day and year.

Understanding Shadow Analysis

Shadow analysis (also called shadow study or shadow impact assessment) is the process of calculating and visualizing how shadows from objects change based on the sun's position in the sky. Because the sun's path varies by location, time of day, and time of year, shadows can look dramatically different from morning to evening and from summer to winter.

The fundamental inputs for shadow analysis are:

Geographic location (latitude and longitude)
Date and time for the analysis
Object heights (buildings, trees, terrain features)
Sun position (calculated using astronomical algorithms)

The sun's position is typically described by two angles: azimuth (the compass direction, e.g., 180° for due south) and altitude (the angle above the horizon, from 0° at sunrise/sunset to 90° directly overhead). Shadow length is inversely proportional to sun altitude—the lower the sun, the longer the shadows.

Who Uses Shadow Analysis?

Architects & Urban Planners

Design buildings that maximize natural daylight. Conduct shadow impact studies required for building permits. Ensure new construction doesn't unfairly shade neighboring properties.

Real Estate Buyers

Evaluate natural light before purchasing. Check if gardens and living spaces get adequate sunlight year-round. Avoid buying properties shaded by neighboring buildings.

Solar Installers

Identify shading that reduces panel efficiency. Even partial shadows can cut output by 30-50%. Plan optimal panel placement by analyzing shadows during peak production hours.

Photographers

Plan shots based on light direction. Find when golden hour creates ideal shadow angles. Pre-visualize how buildings and landmarks will be lit at specific times.

How SunMap Performs Shadow Analysis

SunMap is a free 3D shadow analysis tool that combines several data sources and algorithms:

1
Real Building Data from OpenStreetMap
3D building heights and footprints are sourced from OpenStreetMap, a global collaborative mapping project. This provides accurate geometry for shadow casting.
2
SunCalc Astronomical Calculations
Sun position (azimuth and altitude) is calculated using the SunCalc library, which implements standard astronomical algorithms accurate to within 0.01 degrees.
3
Mapbox GL JS 3D Rendering
Shadows are rendered in real-time using WebGL. Mapbox GL JS calculates shadow projections based on building heights and sun position, displaying them accurately in the 3D map view.

Related Terms

Golden Hour

The period when the sun is 0-6° above the horizon

Sun Azimuth

The compass direction of the sun

Sun Altitude

The angle of the sun above the horizon

Solar Panel Shading

How shadows affect solar energy production

Frequently Asked Questions

How accurate is shadow analysis?

The accuracy depends on building data quality and astronomical calculations. SunMap uses SunCalc for sun position (accurate to ~0.01°) and OpenStreetMap for buildings (varies by region, typically 85-95% accurate for heights in major cities). For legal or engineering purposes, professional surveys may be required.

What is a shadow impact study?

A shadow impact study is a formal analysis required for many building permits. It shows how a proposed building will cast shadows on surrounding properties at different times of day and year. Many jurisdictions have specific requirements, such as analyzing shadows at solstices and equinoxes.

Why are winter shadows longer than summer shadows?

Shadow length is inversely proportional to sun altitude. In winter, the sun takes a lower path across the sky, reaching a lower maximum altitude at noon. This lower angle creates longer shadows. For example, at 40°N latitude, noon shadows in December are about 2.5x longer than in June.

Try Shadow Analysis for Free

Use SunMap to analyze shadows at any location worldwide. No signup required.

Open SunMap