Questions tagged [contour]

Contour maps depict spatially-varying values, such as elevation, by means of curves of equal value.

52
votes
3answers
17k views

Smoothing polygons in contour map?

Here is a contour map for which all the polygons of levels are available. Let ask how to smooth the polygons keeping all vertices preserved in their exact locations? Indeed the contour is made on ...
32
votes
6answers
5k views

How to interrupt contour lines beneath elevation labels (instead of using label buffers)?

Is there a way to interrupt a contour line beneath an elevation label?
32
votes
2answers
38k views

Creating DEM from contours in QGIS?

I have a shapefile with contours and their heights. Is it possible to make a DEM from contours in QGIS without using GRASS? I found Creating DEM from contours using ArcGIS Desktop? but the answer ...
20
votes
5answers
9k views

Placing elevation numbers on contours with uphill orientation and position in QGIS?

I want to orient my elevation labels uphill. Is that possible? I'm currently using the labeling tool from QGIS (not that one in layer settings). I want the labels curved and uphill oriented (and I ...
19
votes
2answers
35k views

Cropping raster layer using QGIS?

How do I crop a raster layer in QGIS? I want to make contours from a section of a layer, and including the whole layer will create far more data than I need and slow down the rendering. I have ...
17
votes
5answers
24k views

Selecting contours which heights are integers?

I have a Contours Featureclass, with an interval of 0.2 meters. I wish to select only those Contours, which are at 1 m interval? I have tried using the following syntax in the 'Select by Attribute' ...
16
votes
3answers
4k views

Generating contours from DEM using GDAL?

We have just received a large set of DEMs at work and I would like to generate contours from them. The DEMs have a resolution of 1m and a size of 1kmx1km. Output from gdalinfo: Driver: AAIGrid/Arc/...
13
votes
2answers
2k views

What is the smallest contour interval possible when derived from a DTM?

I am converting a 2m DTM to contours, and would like to have the smallest interval possible. Is there a theoretical limit, or even a rule of thumb for defining contour intervals based on the ...
12
votes
4answers
8k views

Choosing only one contour line to label in QGIS?

Is it possible to select only one contour line for labelling? I have numerous labels for each line and I'll prefer to label only the main ones, such as 1000 m and 1500 m
12
votes
3answers
19k views

Generating DEM from contour Shapefile using QGIS?

I want to create a DEM from depth contours (shapefile) in QGIS. I've been trying to work out how to do this based on this previous question, notably from this link from that page, however I'm stuck, ...
11
votes
5answers
4k views

Measuring straightness of a curve segment (represented as a polyline)

I'm working on an automatic elevation contour labeling algorithm and one of the factors that I want to take into account when deciding the positions of labels is how "straight" a particular segment of ...
11
votes
2answers
9k views

Convert raster to smooth contour polygons in QGIS

I have had limited success creating smooth contour polygons from a raster layers. I have created contour lines and boundary polylines and then used QGIS Union. Then I use QGIS Polygonize. Then ...
11
votes
2answers
45k views

Creating DEM from contours using ArcGIS Desktop?

I have a large set of contours that I received broken down into several different subsets. I have merged most of the subsets together creating a larger set of contours in three different files. I have ...
10
votes
3answers
21k views

How to create contour lines from point data using QGIS?

I'm using QGIS 2.4.0 and I have a shapefile of points with elevation data and X and Y coordinates. I'm using windows 7 OS. The idea is to create a contour line SHP using my point data. My question ...
10
votes
4answers
2k views

How to automatically plot intermediate contours with QGIS, GRASS GIS or SAGA GIS?

I'm mapping a steep mountain range. My main contour interval is 50 m and my intermediate contour interval is 10 m. In steep areas, the interval of 10 m is too small, so I need to leave ...
10
votes
1answer
1k views

Generating DEM from isolines and spot heights using GRASS?

I have two shape files containing height information of a certain area and I need to create a raster DEM with GRASS using them. file 1 consists of height information in contours (isolines) file 2 ...
9
votes
3answers
2k views

What are common methods for converting raster digital elevation data to vector contours?

In researching this I have found many references to the opposite, creating elevation data from contours, but nothing regarding contour creation. Preferably, I am looking for open source solutions like ...
9
votes
1answer
2k views

Comparison of three contour lines

I am looking for a way to spatially quantify the difference between three contour line shapefiles. More specifically, I have two elevation rasters which I intend to create contour lines from, but ...
9
votes
1answer
945 views

Creating contours with meaningful values from point data

I recently obtained a CSV containing the locations of all recorded bicycle accidents in Boston over the past few years. As an avid cyclist, I'd like to create a simple contour map that draws attention ...
8
votes
3answers
5k views

How to extract slope from topographic raster map? [duplicate]

I am working on a project for a machine learning class wherein I extract features from a topographic raster map and then classify the traversability of the terrain. One of the features I need to ...
8
votes
1answer
1k views

Accurately interpolating elevation from contour lines in QGIS?

I’m trying to interpolate elevations from contour lines (~70000 at 1m intervals, spanning ~20km^2) in QGIS.  When I interpolate using Inverse Distance Weighting (IDW) in the Interpolation plugin it ...
8
votes
1answer
154 views

Why is the “Contour” tool returning contours with an odd rectangular pattern?

I am generating 2' contours made from a smoothed DEM that is 3.2808 foot (1m) horizontal resolution. The result shows these odd squares that are about 80' on a side. The smoothing was done using 8 ...
7
votes
2answers
3k views

How to Create Contours for Zonation

I'm still new in the world of GIS. I'm currently doing some zonation with "test points." Each has its own coordinates and "P" value. I want to make contours of these data, to divide the whole area ...
7
votes
1answer
12k views

Labeling contour lines in ArcMap

Can anybody give me advice on how to label contours as shown in Figure 2 below? I would like to be able to put the label "on" the line, which is easy enough. But I'd also like for the contour line to ...
6
votes
1answer
3k views

Create filled contour map with GRASS

Background I'm trying to make contour/isoline/isochrone maps to show what areas are within walking distance to schools for my pet project to help with the Safe Routes to School program. I followed ...
6
votes
1answer
6k views

QGIS contours smoothing and cleaning

Trying to utilize the contour extraction QGIS tool but having trouble creating smoothed contours. The smooth, generalize, and dissolve tools have not worked for me. Also the plugin for contours ...
6
votes
4answers
7k views

How to install the Python module shapely for QGIS use?

I'm using QGIS 1.8.0 on a Mac with OSX 10.6.8 (Snow Leopard). I've installed QGIS including GDAL, GSL, UNIXImageIO, Freetype, and Matplotlib all from www.kyngchaos.com. When installing the plugin ...
6
votes
1answer
236 views

Splitting polylines in ramps?

I have a shapefile (polylines) of some roads and I want to divide the roads in ramps. Ramp = a piece of the road delimited by the top of a hill and a valley. So, pretending that you're driving in ...
6
votes
2answers
905 views

PostGIS - Interpolate point between contours

Using PostGIS, what is the best method to interpolate the z value for points (the orange dot in the image below) located between each contour layer (blue lines and red lines in the image below)? So ...
6
votes
1answer
1k views

Creating polygon elevation contours?

I'd like to create polygon shapefiles to communicate elevation information on regional maps. I find these draped over a hill shade layer provide one of the best base maps. I can tell some ...
5
votes
2answers
7k views

Colouring areas between (vector) contours?

Is it possible to colour areas between (vector) contours without making it a DEM first? Joshdoe seems to have done so in Create filled contour map with GRASS but does not say how.
5
votes
4answers
679 views

Computing pole of inaccessibility

We are interested at the "Pole of inaccessibility" (https://en.wikipedia.org/wiki/Pole_of_inaccessibility) of our country. Our approach is to use QGIS, and download coastline ([ngdc.noaa.gov]), and ...
5
votes
2answers
9k views

How to perform a slope analysis in QGIS? [duplicate]

I have contour information in the form of line features (see picture below) and I want to do a slope analysis in QGIS. Is it possible?
5
votes
1answer
662 views

Styling contours at specific numbers [duplicate]

I have a contour vector layer with a step 0.2m . I want every 1 metre, to change the line style, a thicker line for example, and the rest of them,symbolize with a dotted style. So, I can do it ...
5
votes
2answers
2k views

How to replace pixel values in a single band DEM?

I have a single band DEM as a GeoTiff. I would like to replace values above or below a certain threshold with 0. Can I do that with GDAL?
5
votes
2answers
1k views

How to specify gdal_contour output format as postgresql table?

I want to generate contours with gdal_contour command. It generates an output as shapefile by default. I want this utility to output a postgresql (postgis) table. The documentation says there is a -f ...
5
votes
3answers
2k views

How to position contour labels in Maplex above the line?

I would like to utilize the "contour placement" options of "Uphill alignment" and "Laddering" while positioning the label above the contour not over it. This does not seem to be an option under the ...
5
votes
1answer
1k views

QGIS - Create single contour line at specific height from DEM

I wish to create a single contour line of height 4.54 m from a DEM layer. Any idea how I may do this please?
5
votes
1answer
2k views

How to create contours from smoothed DEM instead of using Terrain to Raster?

I'm fairly new to working with lidar and have been assigned the task of creating 2ft contours for the entire county using USGS-provided lidar tiles. Is there a significant difference in the accuracy ...
5
votes
2answers
594 views

Using field calculator to delete specific contours

I have 3 contour shapefiles with 25m, 50m and 100m equidistance. Now I want to delete in the 25m-shp-file every **50m and **00m contour and in the 50m-shp-file every **00 contour. How can I show them ...
5
votes
2answers
3k views

Postgis 2.1: ERROR: Shell is not a line - SQL state: XX000

My current setup is PostgreSQL 9.3.6 & PostGIS 2.1.5 I have a table with contour lines (multilinestrings) that I wish to group by the attribute 'elevation', and make polygons out of them. The ...
5
votes
2answers
2k views

Creating contours for specific elevations

Input data: 1. an SRTM raster. 2. Point file of peaks. -Attributes contain ID, x, y, z and the elevation at which the peak is completely isolated from a neighboring peak. The output I want is a line/...
5
votes
2answers
2k views

Finding depression with contour lines

How can I find depression contour lines? I already have find depressions via Fill-method, but now I try to detect them by using the contour lines, anyone have an idea ?
5
votes
1answer
1k views

Obtaining a contour as a single polygon in ArcGIS?

I have a DEM that I want to retrieve a single contour polygon from at a given elevation. I can use the Contour tool to obtain a series of polylines at a given elevation by setting the contour interval ...
5
votes
1answer
298 views

Trying to Create Tanaka Contours in QGIS

I am following a tutorial with which to create Tanaka contours from: Tanaka Contours. I used contour with the default 10 increments setting. Below are the raster and resulting contours. Following ...
5
votes
1answer
590 views

How to find depressions (sinks) and hills based on contour line features

I have contour lines (interval 0.1m), derived from a DEM (1m). I used the thinning ratio to find only features, which are like circles. I've imported these features into a Spatialite database. The ...
5
votes
1answer
2k views

Contour lines with imported shapefile using Blender GIS - wrong Z values

I've been making experiments with Blender GIS and QGIS. I'm having problems when importing Shapefiles with contour lines, with a field for elevation (ELEVATION FROM FIELD selected when importing). I'...
5
votes
1answer
957 views

Generating a vector contour map of fictional terrain

Originally I had asked this on the Graphics Design SE but after some realization of the question I was asking, it's probably better to ask it here. I'm making a fantasy world map in illustrator that ...
4
votes
1answer
2k views

Producing smooth and consistent contour lines from SRTM

I downloaded and merged together a set of SRTM imagery. I am not sure whether it is my workflow, the actual terrain in question or if the scale of the imagery is simply too large to obtain smooth ...
4
votes
1answer
161 views

Summing attributes of different shapes into another (height of contours + height of buildings)

I'm using QGIS 2.18. I need to calculate the height of the rooftop of each building in a neighborhood. I have a vector shape of the buildings, with the building height attribute (from the ground to ...