GEOM1004-spatial_analysis-W22

Overview of Spatial Analysis of GIS Data

Spatial analysis within Geographic Information Systems (GIS) can be broadly categorized into various types of operations, including vector and raster operations. Each type serves different analytical purposes, enabling users to manipulate and analyze spatial data effectively.

Vector Operations

• Vector Operations Flowcharting: Understanding the flow of vector operations is crucial for effective GIS analysis. The basic operations include:

  • Intersect: Combines features from two layers and returns only the overlapping areas.

  • Union: Merges two layers and includes all features from both.

  • Erase: Removes portions of features based on another layer.

  • Symmetrical Difference (XOR): Returns features from both layers excluding overlapping areas.

  • Identity: Returns features from one layer with attributes of overlapping features from the other.

  • Clipping: Applies one layer of spatial data to another, effectively cutting out sections.

Raster Operations

Raster operations also form an integral part of spatial analysis and can be divided into:

• Local Operations: These work on single cell locations, modifying each cell independently based on its value.

• Focal Operations: These consider the cell and its neighbors (neighborhood) to create a result based on surrounding cell values, using methods such as moving windows.

• Zonal Operations: Analyzes cells located within defined zones to calculate statistics or modifications based on their properties.

Importing and Buffering Data

Buffering involves creating a zone around a point, line, or area feature. This can be done using either a raster or vector data model, with common applications noted as:

• The creation of polygons around point features (like building centroids) at specified distances (e.g., 10m, 30m).

• Vector buffering typically achieves this more effectively. For example, a 10 m buffer around a road network can be created without or with dissolve operations.

Boolean Logic in Vector Operations

Understanding boolean overlay logic is foundational for executing vector operations accurately. The core operations include:

• A AND B (Intersection): Returns features common to both layers.

• A OR B (Union): Merges features from both layers without losing any.

• A NOT B (Erase): Subtracts features of B from A.

• A XOR B: Features the unique to each layer but excludes overlaps.

Practical Applications

Tasks Examples

1. Buffer Creation: A task might involve creating a buffer zone around roads to identify safe distances for environmental studies.

2. Point-in-Polygon Analysis: This type of analysis figures out which points fall within specific polygons, such as determining which borrows pits in an area correspond to specific soil types.

3. Slope and Aspect Calculations: Identifying the slope and aspect of terrains, which assist in understanding drainage, exposure to sun, and other environmental factors influencing land use.

GIS Workflow for Specific Analysis

• Wetlands Project Example: For a project identifying wetland areas suitable for UAV surveys: combine small roads features with wetland shapefiles and apply buffer and erase operations to remove unsuitable locations near major roads.

• Spatial Analyst Role: Utilize tools like ArcToolbox and Spatial Analyst to perform computations such as raster calculators for local operations, ensuring the analysis is both efficient and effective.

Zonal Statistics

Zonal statistics allow the extraction of statistical measures (mean, sum, etc.) from zones defined in your analysis, facilitating a deeper understanding of spatial patterns across areas like parks or development zones. Reports can summarize crucial insights from these statistics, supporting decision-making processes.

Conclusion

The various operations and techniques highlighted above confirm GIS as a powerful tool in modern spatial analysis. Understanding vector and raster analyses through applicable operations and real-world tasks is essential for effective GIS use.