Spatial Analysis Workflows

Lesson 6 of 8 · GIS Software Fundamentals · Beginner

Spatial analysis uses geographic relationships to answer questions that cannot be answered by looking at a table alone. Before running any analysis, define your question clearly — the right tool depends on what you are trying to find out.

Define the Question First

Spatial analysis tools are powerful, but they produce results whether or not those results are meaningful. Starting with a clear question prevents wasted effort and misinterpretation. Ask: What am I trying to find out? What inputs do I need? What does a correct result look like?

Common Spatial Operations

Buffer

A buffer creates a zone of a specified distance around features. A 500-metre buffer around transit stops creates a polygon showing the area within 500 metres of each stop. Buffer distance must be in the units of your CRS — if your data is in a geographic CRS (degrees), buffer distances in metres will not work correctly. Use a projected CRS for buffer analysis.

Intersection

An intersection keeps only the features or areas that fall within both input layers. Intersecting a parks layer with a neighbourhood boundary layer produces only the park areas within that neighbourhood.

Clip

Clipping cuts one layer to the extent of another. Clipping a roads layer to a study area boundary produces only the road segments within the study area.

Dissolve

Dissolving merges features that share a common attribute value into a single feature. Dissolving a parks layer by park_type produces one polygon per park type, combining all parks of the same type.

Spatial Join

A spatial join transfers attributes from one layer to another based on geographic relationship. Joining transit stops to neighbourhood polygons adds the neighbourhood name to each transit stop record. Spatial joins can create duplicate rows when one feature matches multiple features in the other layer — always check the output record count.

Consistent Example: Facilities Near Transit

You want to identify public facilities in Riverton within 400 metres of a transit stop. Workflow:

1. Confirm all layers are in the same projected CRS.
2. Create a 400-metre buffer around each transit stop.
3. Use a spatial selection or intersection to find facilities within the buffer zones.
4. Check the output — how many facilities were found? Do they appear in expected locations?
5. Review any unexpected results before drawing conclusions.

Preserving Source Data

Always run analysis on copies or save outputs to new files. Never overwrite your source data with analysis results. Name output files clearly, including the operation and date if helpful.

Validating Output

Spatial analysis output requires validation. Check:

• Does the output extent look correct on the map?
• Does the record count make sense?
• Are there unexpected duplicate records?
• Do the attribute values in the output match what you expected?

Different analysis settings — different buffer distances, different spatial relationship types — produce different results. Document your choices so the analysis can be reproduced or reviewed.

Common Mistakes

• Running a buffer in a geographic CRS and treating the result as metres.
• Not checking for duplicate rows after a spatial join.
• Overwriting source data with analysis output.
• Accepting output without validating it against known reference points.
• Choosing analysis parameters without documenting them.

Key Takeaways

• Define your question before choosing an analysis tool.
• Common operations include buffers, intersections, clips, dissolves, and spatial joins.
• Buffer analysis requires a projected CRS with distance units in metres or feet.
• Spatial joins can produce duplicate rows — always check output counts.
• Validate all analysis output before drawing conclusions.