I'm trying to reproduce the steps needed to aim this goal: Given a layer of polygons, I'm want to retrieve for each polygon which is at a distance less than 50m to a 2nd polygonal layer the only 5m band in the polygon facing the items of the second layer. A drawing may be a better way to explain myself. I want to build the red parts (the 5m band of the orange layer polygons facing the green ones, when they're at a distance less than 50m). How would you do that with QGIS?
123455
I'm trying to reproduce the steps needed to aim this goal: Given a layer of polygons, I'm want to retrieve for each polygon which is at a distance less than 50m to a 2nd polygonal layer the only 5m band in the polygon facing the items of the second layer. Quite complicated explanations...I know....so, a drawing is a better way to explain myself. I want to build the red parts (the 5m band of the orange layer polygons facing the green ones, when they're at a distance less than 50m)....How would you do that with QGIS?
101741
I've been having trouble with this particular problem, been thinking for it for a good hour or two, but I haven't gotten an explanation to the following question.  Suppose $a_n$ be the number of regions into which a convex polygonal region with $n+2$ sides is divided by its diagonals, assuming no three diagonals have a common point. Define $a_0 = 0$. Show that   $$a_n = a_{n-1} + {n+1 \choose 3} + n \quad (n \geq 1)$$  So far, I have that for $n \geq 1$, we look at an $(n+2)$-gon. Pick an edge from one of the $n+2$ edges from the $(n+2)$-gon. Then adjoin a triangle to it, so we can have an $(n+3)$-gon. Given the triangle that we adjoin to the $(n+2)$-gon, let's look at the exposed vertex of that triangle. We can create $n$ diagonals, since we can't create a diagonal by joining the exposed vertex to an adjacent vertex. So now, we have that $n$ diagonals run through the edge created by the intersection of the $(n+2)$-gon and the triangle. This gives us $n+1$ regions in the triangle. But now, I can't seem to find a pattern to why the $(n+2)$-gon has ${n+1 \choose 3}$ extra regions that is as a result of those $n$ diagonals traversing through the $(n+2)$-gon. Any tip or hint would be appreciated.
52323
Is there an option in QGIS to fill holes in polygons automatically by setting parameters e.g. maximum area, distance between borderlines? I want to delete/fill holes that a very &quot;thin&quot;/small.
89830
I'm using QGIS 1.8 with a PostGIS database and I have three PostGIS-layers in QGIS a lines layer, a points layer and a polygon layer.  What I'm trying to do is to select a polygon in the polygon layer and mark all points within this polygon.   For me the only way to do this is to use the button "Select by Polygon" but in this way, I cannot use an existing polygon for selection.
91538
I have a Shapefile with Polygon features  representing the world's land areas (continents, islands).   Is it possible to invert these, and get a geometry that represents the world's oceans and seas?   So the original land Polygons need to become rings in a single global Polygon that covers the planet.  Basically, I'm looking for something like Select > Inverse in Photoshop.   I am using QGIS.
94444
I'm new to QGIS. In my project i have two layers: one is my vector (city boundaries) and the other is the OSM (obtained with the plugin). How can I cut the OSM along the edges of the vector? I want to obtain only a region of the map, to save it as an image.
105436
I have a polygon vector layer and a line vector layer in a form of grid (they are both in the .shp format). I need to split polygons by these lines.   I tried digitizing tools but the problem is that it deals only with 1 line at a time and I have more than 52,000 lines. It will take a ridiculously long time to split it manually. How can it be done for all the lines?   I have QGIS 2.18.
26142
I have a Shapefile (polygon), I need to calculate distance (Node to Node) along the lines in map unit(meter or kilometer).  I want to do it in ArcGIS.
53830
I created a simple service layer polygon in network analyst (ArcGIS Desktop 10.2) with no hierarchies set in the street network. Now I don't understand why is this polygon created along some particular streets?   Why isn't is properly spread out? For example, why doesn't the polygon cover the areas/streets I have marked in red? Obviously those marked areas are also within 1 km.  The impedance is 1 km and 2 km respectively.   The streets are also well connected individual line elements as you can see the junctions.
41713
I have two layers, one (A) has point features and the other (B) has polygons.  How do I produce a new table with some (the ID) or all the fields from the A table and some (the area code) or all from the B table where the B polygon contains the A point?  I am using QGIS.
33537
I actually did this a few weeks ago but I can't remember how.  I want to create points on the perimeter of a set of polygons at a specific distance interval. I am using ArcMap.  I could do Polygon Vertices to Points, but that would only give me points on the vertices, which I don't necessarily want. What I want is a regular set of points on the perimeter of the polygons.  This is my base polygons:    And this is what I would like to get (the points at regular intervals):    Any ideas?
16607
I work with this polygon and try to find a way to create a new polygon from the empty gap (not distinguish it) in the middle of the polygon.  I succeed to do it with a "Difference" tool but used with another layer on the polygon and then using the difference tool.  I can also digitize the shape of the hole and create a new layer I seeking an automated way to do it and not doing in manually.   I read:        Is it possible to do it with a direct tool in QGIS 2.18.1, without the aid of another layer?
36604
I recently looked at some  relating to this topic but as far as I can tell there is currently not a working plugin or script for QGIS 2.0 to achieve a four color theorem for styling polygon vector data (it doesn't necessarily have to be 4 colors, just so that each neighboring polygon is a different color, though keeping it at a minimum number of 4-6 colors would be elegant).
105745
I have a polygon layer on top of a DEM.  Is there a way to clip the polygon layer according to elevation, ie the clipped result being only those areas of the polygon layer between x and y altitude?  The result needs to be a vector layer.
109214
I was looking at * and started thinking about the case of a polygon with 4 sides: a square.   The question asks for a program that can take a polygon of N sides and return the smallest possible polygon of N-1 sides that contains the original polygon.  Thinking about it, I wasn't sure what the optimal triangle encapsulating a square would look like. In KSab's answers, he returns a triangle that looks like this:    This area is 2*(area of the square). With some easy guess-and-check work I found that this seems to be optimized. How do you prove that there is no better solution?  EDIT: another consideration for the orientation of the triangle could be this:
68443
I'm trying to convert sets of points to their respective polygon boundaries.  I think this is something like a Voronoi diagram or Convex Hull, but not quite.  I'm sure there's a technical term for it, but I'm a beginner to GIS.  It's probably best illustrated with the following image:    So, given 4 sets of points (each set in its own colour), what are the four polygons surrounding each respective set of points such that the spacing between polygons maximizes the margins and all the polygons meet together?  Here's a simplified example with 3 points:   A,43.656943,-79.393928,blue B,43.66663,-79.402682,green C,43.656447,-79.408004,green   You'll have to view the following graphic for it to make sense:   Essentially, each point has a colour and you expand a buffer of a certain distance out from it to start.  The hard part is when there's a collision with other points (their boundaries) and where to compute that boundary. The result is a set of polygons (one for each colour/set).
240
I have a point shapefile of villages where data was collected in Northern Kenya. I created a buffer around those villages.   The second vector layer contains polygons defining areas according to vegetation type. So for example, a forest might be surrounded by a narrow ring of woodland in an area which is mainly grassland. I'm trying to obtain a percentage of each vegetation type within the buffer per village.   I'm using QGIS 1.7