Browser-only GIS analysis
Uploaded shapefiles are processed locally and are not saved to Flowpath.
0. Upload GIS layers
Layer 1
Catchment boundary
Select all files for the sub-catchment boundary shapefile.
Click or drop shapefile parts here.
.shp.dbf.prj optional
Layer 2
Impervious surfaces
Select all files for roads, buildings, paving, and other hard surfaces.
Click or drop shapefile parts here.
.shp.dbf.prj optional
Upload note: a shapefile is a set of files. For each layer, select the `.shp`, `.dbf`, and preferably `.prj` files together. The `.shx` and `.cpg` files can also be included when available.
1. Analysis results
Upload both shapefile layers, then click Calculate.
2. Catchment visualisation
Run an analysis to preview the catchment outline.
3. Methodology and assumptions
The tool reads the uploaded boundary and impervious shapefiles in the browser, reprojects supported New Zealand coordinate systems to WGS84, dissolves the catchment boundary, clips each impervious polygon to that boundary, and divides the clipped impervious area by the catchment area.
- Supported CRS detection includes Mount Eden 2000, NZTM2000, NZMG, and WGS84.
- The `.prj` file is used first when available; coordinate ranges are used as a fallback.
- Invalid or non-polygon features are skipped and reported in the warning list.
- Overlapping impervious polygons may double-count area unless they are dissolved before upload.