# GIS for Site Analysis
Geographic Information Systems (GIS) enable architects to analyse, visualise, and interpret spatial data for informed site decisions. By layering geographic datasets — topography, hydrology, transport networks, land use, environmental constraints — GIS transforms raw spatial information into actionable design intelligence. For the practicing architect, GIS bridges the gap between desktop design and the physical, regulatory, and environmental realities of a site.
---
## Table of Contents
- [GIS Fundamentals for Architects](#gis-fundamentals-for-architects)
- [Spatial Data Types](#spatial-data-types)
- [Coordinate Systems and Projections](#coordinate-systems-and-projections)
- [Terrain and Topographic Analysis](#terrain-and-topographic-analysis)
- [Solar and Shadow Studies](#solar-and-shadow-studies)
- [Viewshed and Visibility Analysis](#viewshed-and-visibility-analysis)
- [Environmental Constraint Mapping](#environmental-constraint-mapping)
- [Site Suitability Analysis](#site-suitability-analysis)
- [GIS Tools for Architects](#gis-tools-for-architects)
- [Integration with Design Software](#integration-with-design-software)
- [See Also](#see-also)
---
## GIS Fundamentals for Architects
| Concept | Description |
|---------|-------------|
| **Spatial Data** | Information linked to geographic coordinates |
| **Georeferencing** | Assigning real-world coordinates to data |
| **Layer Stacking** | Overlaying multiple datasets for combined analysis |
| **Attribute Table** | Tabular data attached to spatial features |
| **Spatial Query** | Selecting features based on location or relationship |
| **Buffer Analysis** | Creating zones at specified distances from features |
| **Geoprocessing** | Operations that transform spatial data (clip, merge, intersect) |
---
## Spatial Data Types
| Type | Format | Description | Example |
|------|--------|-------------|---------|
| **Vector — Point** | SHP, GeoJSON | Discrete locations | Trees, boreholes, utility poles |
| **Vector — Line** | SHP, GeoJSON | Linear features | Roads, rivers, utility lines |
| **Vector — Polygon** | SHP, GeoJSON | Bounded areas | Plot boundaries, building footprints, zones |
| **Raster** | GeoTIFF, DEM | Grid of cells with values | Elevation models, satellite imagery |
| **LiDAR Point Cloud** | LAS, LAZ | 3D point measurements | Detailed terrain, existing building geometry |
| **Mesh/TIN** | Various | Triangulated irregular networks | Terrain surfaces for 3D visualization |
---
## Coordinate Systems and Projections
| System | Coverage | Use |
|--------|----------|-----|
| **WGS 84 (EPSG:4326)** | Global | GPS coordinates, web mapping |
| **UTM Zones** | Regional (6° strips) | Large-area site mapping |
| **British National Grid (EPSG:27700)** | UK | OS mapping, UK planning |
| **State Plane** | US states | Local surveying in the US |
Architects must ensure all datasets share the same coordinate reference system before overlay analysis.
---
## Terrain and Topographic Analysis
| Analysis | Output | Design Application |
|----------|--------|-------------------|
| **Contour Generation** | Contour lines at set intervals | Site grading, building placement |
| **Slope Analysis** | Slope gradient map (degrees or %) | Buildability, access road routing, drainage |
| **Aspect Analysis** | Direction of slope face | Solar orientation, microclimate |
| **Cut and Fill** | Volume calculations | Earthwork estimation, cost |
| **Watershed Delineation** | Drainage catchment boundaries | [[Stormwater Management]] planning |
| **Hillshade** | Shaded relief visualization | Terrain communication, presentation |
### Slope Classification for Development
| Slope | Classification | Development Suitability |
|-------|---------------|------------------------|
| 0–5% | Flat to gentle | Ideal for most building types |
| 5–10% | Moderate | Suitable with grading, split-level design |
| 10–15% | Steep | Requires significant earthwork, terracing |
| 15–25% | Very steep | Limited development, specialist foundations |
| >25% | Extreme | Generally unsuitable for buildings |
---
## Solar and Shadow Studies
GIS-based solar analysis maps solar radiation across a site accounting for terrain, latitude, and surrounding obstructions:
| Analysis | Description |
|----------|-------------|
| **Solar Radiation Map** | Annual/monthly kWh/m² across site surface |
| **Shadow Casting** | Hour-by-hour shadow patterns from terrain and buildings |
| **Solar Envelope** | Maximum buildable volume that preserves solar access to neighbours |
| **Photovoltaic Potential** | Roof/ground areas suitable for [[Solar Photovoltaic Systems]] |
These analyses connect directly to [[Passive Solar Design]] and [[Solar Shading Design]] strategies.
---
## Viewshed and Visibility Analysis
| Analysis | Application |
|----------|-------------|
| **Single-Point Viewshed** | What can be seen from a specific observation point |
| **Multi-Point Viewshed** | Combined visibility from multiple locations |
| **Visual Impact Assessment** | How a proposed building appears from key viewpoints |
| **Line of Sight** | Binary visibility between two specific points |
| **Cumulative Visibility** | Number of viewpoints from which a location is visible |
Viewshed analysis is critical for planning applications, heritage settings, and landscape-sensitive projects.
---
## Environmental Constraint Mapping
| Constraint Layer | Data Source | Design Impact |
|-----------------|-------------|---------------|
| **Flood Zones** | EA, FEMA flood maps | Building setbacks, floor level, flood resilience |
| **Protected Habitats** | Natural England, EPA | Development exclusion zones, ecological mitigation |
| **Contaminated Land** | Local authority registers | Remediation requirements, foundation design |
| **Noise Mapping** | Strategic noise maps | Facade acoustic design, building orientation |
| **Air Quality** | DEFRA, EPA monitoring | Ventilation strategy, [[Indoor Air Quality Standards]] |
| **Heritage Zones** | Listed buildings, conservation areas | Design restrictions, material constraints |
| **Utilities** | Asset owner records | Easements, diversion costs |
---
## Site Suitability Analysis
Multi-criteria site suitability analysis combines weighted constraint layers:
1. **Define Criteria** — Slope, flood risk, access, land use, ecology
2. **Classify Layers** — Score each criterion on common scale (1–5)
3. **Assign Weights** — Reflect relative importance of each criterion
4. **Overlay** — Weighted sum or weighted product combination
5. **Map Output** — Suitability heat map highlighting optimal zones
This method directly informs [[Site Analysis and Response]] during early design stages.
---
## GIS Tools for Architects
| Tool | Type | Cost | Strengths |
|------|------|------|-----------|
| **QGIS** | Desktop | Free/open-source | Full GIS capability, extensive plugins |
| **ArcGIS Pro** | Desktop | Commercial | Industry standard, advanced analysis |
| **ArcGIS Online** | Cloud | Subscription | Web mapping, collaboration |
| **Google Earth Pro** | Desktop | Free | Quick site overview, historical imagery |
| **Mapbox** | Web API | Freemium | Custom web maps, 3D terrain |
| **Grasshopper + Heron** | Plugin | Free | GIS data import into Grasshopper |
| **Ladybug Tools** | Plugin | Free | Environmental analysis in Grasshopper |
---
## Integration with Design Software
| Pathway | Description |
|---------|-------------|
| **QGIS → Rhino** | Export shapefiles/DXF, import into Rhino for 3D modeling |
| **Heron (Grasshopper)** | Stream GIS data (OSM, terrain) directly into parametric environment |
| **Elk (Grasshopper)** | Import OpenStreetMap data into Grasshopper |
| **Civil 3D** | Native GIS/survey data handling for site engineering |
| **Revit Site Tools** | Limited; better to prepare terrain in Civil 3D or Rhino |
| **GIS → BIM** | Georeferenced BIM models aligned with GIS coordinate systems |
---
## See Also
- [[Site Analysis and Response]]
- [[Urban Data Analytics]]
- [[Remote Sensing for Architecture]]
- [[Spatial Data in Design]]
- [[Bioclimatic Architecture]]
- [[Passive Solar Design]]
- [[Urban Design Fundamentals]]
---
#gis #site-analysis #spatial-data #terrain #environmental-analysis #digital-practice