# Tag Info

Accepted

### Create a circle of defined radius around a point and then find the overlapping area on a shapefile

I think this should do what you want. Essentially what I mentioned in my comment. One thing I didn't mention is that you will want to transform to an appropriate equal-area projection that uses ...
• 246

### Calculating polygon area using 2 methods in QGIS

The reason is that \$area is calculating the geographic area which takes into account the curvature of the earth, while the other method is calculating the planimetric area which does not account for ...
• 6,150
Accepted

### Voronoi that don't cross boundaries

The buzzwords are shortest path voronoi diagram, voronoi tessellation with constraints, conforming tesselation or restricted tesselation. CGAL could help you to combine a constrained triangulation ...
• 3,603

### Hack's law for river basins

Hack's law, for a set of sub-basins, relates the length of the longest stream in each basin to the basin catchment areas. We effectively need to measure the longest upstream channel and the catchment ...
• 11.1k

### Buffering with obstacles

EDIT : Faster processing direcly with geometries From : To : With (description in the code comments) : def buffer_dist(lyr_input, distance: int): """Create a buffer from the ...
• 15.8k
Accepted

### Buffering with obstacles

There are two possibilities that come to mind. The first is to use isochrone instead of buffer (there are numerous online services that will calculate them for you, some of them are discussed here). ...
• 16.7k

### Buffering with obstacles

An alternative technique using standard spatial analyst tools in ArcGIS Pro or ArcMap is to use the Euclidean distance tool and set the lines as barriers and a maximum distance. This would create such ...
• 43.9k
Accepted

### Delineating multiple nested catchments in R whitebox; prevent primary catchment from being cut by subcatchment

This scenario is precisely what the WhiteboxTools UnnestBasins tool is used for. The tool documentation states: In some applications it is necessary to relate a measured variable for a group of ...
• 11.1k
Accepted

### How to calculate areas of land cover from a File System Raster?

If you have the Spatial Analyst extension available, I think that the Tabulate Area tool will do what you're looking for. If you specify your polygon feature class/shapefile as the "Input feature zone ...
• 1,566

### PgRouting coverage area with node restrictions

You can simply join your vertices to edges and then use vertex close/open information to set edge cost acordingly. I supose your graph is directed, so then you want only left join on target vertex ...
• 1,353

### Creating catchment from point using DTM raster in QGIS?

You can use Saga "Upslope area" geoalgorithm. You must install Saga and configure the path where you installed Saga inside QGIS in Processing->Options or Ctrl+Alt+C. Then expand Providers->Saga,...
• 1,041
Accepted

### QGIS: Saga Channel network: how to prepare SRTM data

You might want to try running Fill Sinks. This is available using SAGA via Processing. There may be GRASS versions too. I didn't see any mention of it in the tutorial you linked to, so it's worth a ...
• 20.5k
Accepted

### How can one compute the proportion of a country's area that lies within a given distance from the country's border?

Actually, you can buffer the polygon itself. You will need to reproject your administrative area polygon's CRS (as many vector data sets are provided in EPSG:4326 (WGS84), with 'units' in latitude/...
• 30.5k
Accepted

### Calculating population in catchment area in QGIS

If I understand correctly, you want to know how many people live within a given time-based distance from your points. For instance, how many people live within 5min of a mailbox. Based on the ORS ...
• 696
Accepted

### How to create a buffer for catchment area of an historical settlement

you could use the r.walk.coords GRASS algorithm using processing (available in 2.18, may not be available in older versions). According to the documentation this uses Naithsmith's rule which iant ...
• 20.5k
Accepted

### Catchment area map automatic creation

Sounds like you are looking to construct Voronoi polygons on the sphere. Given a set of points, the Voronoi polygon of a point of the set is the polygon that contains an area where that point is the ...
• 65.4k
Accepted

### Splitting catchments in GRASS

To use GRASS you need to have the raster of flow directions inside the catchement area A. I will assume you do not have it yet and I will present all required steps as they can be perfomred in QGIS. ...
• 3,240

### Splitting catchments in GRASS

If you want to split the polygon manually you can use split feature tool in QGIS from Advanced Digitizing Toolbar . You can enable Advanced Digitizing Toolbar from View → Toolbars → Advanced ...
• 41.2k
Accepted

### how can interior basins be modified in the r.watershed GRASS function?

Unfortunately, the answer is no, you cannot. From what I understand of the fuction r.watershed, the subbasins cannot be merged, which is what I guess you want to happen. I understand your question ...
• 3,240

### pgr_drivingDistance How to split edge if max distance is reached halfway through the edge (PGROUTING)

I'm sure there is other, maybe simpler way, but I did it as follows: created new table (t1) using driving distance created another table as select from t1 with all edges which have cost < defined (...
• 2,617

### Network analysis using QGIS?

The easiest way (at least for me) was to use GRASS for this. In QGIS you load the road network and the points (bus stops). Open the tool box (Str+Alt+T) next and search for v.clean and v.net.iso. You ...
• 465

### PgRouting coverage area with node restrictions

pgRouting's network topology does not handle nodes but only edges, so you have to apply costs of the nodes to the edges.
• 4,796

### Splitting up polygon with grid using QGIS

Invalid geometry suggests that your source data may have some problems with it. One or more of the records has a geometry which is - ironically - invalid. Invalid geometry may be caused by self-...
• 3,576

### Hydrological catchment area for a road segment (QGIS)

You cannot, I believe, calculate upstream drainage area for a line feature. A road segment could, for example, cross over a ridge such that parts of the line segment would be in one watershed, and ...
• 15.7k
1 vote

### Why does running the SAGA Upslope Area tool in QGIS result in a 0 (zero) to 0 (zero) histogram and an all black layer?

What finally worked for me was zooming in and capturing the coordinates of a point precisely in a channel. Points near but not in a channel had given me upslope areas too small to see.
• 11
1 vote

### Why does running the SAGA Upslope Area tool in QGIS result in a 0 (zero) to 0 (zero) histogram and an all black layer?

The SAGA Upslope Area tool has worked for you correctly, though you would be seeing the black output layer (Upslope Area), plus Min=0 and Max=0 statistics in its Symbology panel. Change the Max ...
• 31k
1 vote
Accepted

### Population in upstream area (looping over FeatureCollection)

You'll need to map over all your stations and based on that geometry (points) select the relevant hydro features. If you create a union of those features you'll have to apply a reduceRegion only 1 ...
• 2,073
1 vote
Accepted

### GRASS Error: WARNING: segment zero_fill(): Unable to write (No space left on device)

After trying many things, I found that the solution was simpler than I thought. Despite the terrain data was relatively coarse (30m), the region settings in grass were defined at a 1m x 1m resolution. ...
• 604
1 vote

### Delineating service catchment in QGIS?

This sounds like a problem for PyQGIS. I'm a total Python newb, so it would take me a very long time to actually code this, but I outlined a possible solution in pseudocode. # Add a unique ...
• 24.9k
1 vote

### Error in catchment area calculation

Following Kazuhito's comment, I installed SAGA 2.1.4 and the algorithm produced a raster layer. However, I am not sure if the algorithm ran properly because during the process, some errors were ...

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