Clip vs Intersect vs Dissolve: Choosing the Right Vector Operation

If you've ever run an operation expecting one result and gotten something that looks almost right but isn't quite what you needed, there's a good chance it was one of these three. Clip, Intersect, and Dissolve all involve cutting or combining polygons, which is exactly why they're so easy to confuse — but they answer three genuinely different questions, and picking the wrong one usually means starting over.

The short version

Before the details: if you're trying to cut one layer down to an area of interest, you want Clip. If you're trying to find where two layers genuinely overlap, and keep data from both, you want Intersect. If you're trying to merge adjacent shapes within one layer that share something in common, you want Dissolve. The rest of this guide goes through each one properly, since "cut" and "overlap" and "merge" can still sound interchangeable until you've seen the actual difference on real data.

Clip — cutting one layer to a boundary

Clip takes two inputs: the layer you want to cut (the input), and the layer that defines the boundary you're cutting it to (the clip layer, often called an area of interest or AOI). The output keeps only the parts of the input layer that fall inside the clip boundary — and critically, it keeps only the input layer's own attributes. The clip layer's attributes never appear in the result; it's purely a cookie-cutter.

A real example: you have a national roads network and a single district boundary. Clipping the roads to the district gives you just the roads within that district, with all their original road attributes (name, class, surface type) intact — and nothing from the district boundary itself carried over, since you likely don't need it.

Intersect — finding genuine overlap between two layers

Intersect also takes two layers, but the relationship is symmetric, not one cutting the other. The output contains only the areas where the two inputs genuinely overlap, and — this is the real, important difference from Clip — the attributes of both layers are combined in the result. Intersect also isn't limited to polygon-on-polygon the way people often assume; it works between any real combination of geometry types (a line intersected with a polygon gives you the portions of the line inside the polygon, for instance).

A real example: you have a soil-type layer and a land-parcel layer, and you genuinely need to know which soil types occur on which specific parcels. Intersecting them gives you a new set of polygons — each one a genuine overlap between one soil type and one parcel — carrying both the soil attributes and the parcel attributes together. Clip alone couldn't give you this, since it would only preserve one layer's data, not both.

Dissolve — merging shapes within one layer

Dissolve is fundamentally different from the other two: it only ever looks at one layer, not two. It merges polygons that are adjacent or overlapping and share the same value in a field you choose, removing the boundary lines between them and producing one larger polygon per unique value. Anything not sharing a border with another polygon of the same value simply stays as its own separate feature in the output.

A real example: you have a parcel layer where every parcel carries a "Zoning" field (Residential, Commercial, Industrial). Dissolving on that field merges every group of adjacent same-zoning parcels into single, unified zoning-district polygons — genuinely useful for a zoning map, where you want to see districts, not hundreds of individual parcel lines. The Residential parcels in one part of town and another, unconnected part of town would correctly stay as two separate output features, since they don't share a border.

Putting them together — a real, combined workflow

These three genuinely compose well together, and a real project often uses more than one in sequence. A common, real pattern: Clip a large statewide layer down to your actual project area first (so you're not processing data you don't need), Intersect it with a second, relevant layer to combine the attributes you actually need answered, then Dissolve the result on whichever field defines the final categories you want to map or report on.

How to do it

1. Upload your layer(s)

   Real shapefile folders (all component files together, no manual zipping), GeoJSON, or GeoPackage — Clip and Intersect take two layers, Dissolve takes one.

2. Pick the operation and configure it

   For Dissolve, choose the field to dissolve on. For Clip and Intersect, confirm which layer plays which role.

3. Run and export

   Get the real result back in your choice of format — Shapefile, GeoJSON, GeoPackage, and more — with a correct, clean attribute table.

Beyond these three

The same Vector Analysis Toolkit that handles Clip, Intersect, and Dissolve also covers Union, Erase, Buffer (simple, by-feature, and multi-ring), Centroid, Convex Hull, Simplify, Spatial Join, Nearest Feature, Area/Length calculation, and Point-in-Polygon Count — 15 real operations in total, all in the same place.