Generating Contours from  DEM in QGIS

Generating Contours from DEM in QGIS

GIS, QGIS, Software, Tutorials
      A few weeks ago I wrote a post on “Generating DEMs from Contours” which was quite a straight forward process as explained.In this post , I will show how to “reverse engineer” the process and generate contours from DEMs. This time round am also going to demonstrate how to clip our dataset to work with the area of interest instead of working on the whole dataset. Lets begin: Assumption: You have the DEM on your local machine. If not so, data can be downloaded from either USGS EarthExplorer or from GeoComm Steps: Launch QGIS 2.X and Load our Raster Layer (DEM) i.e. Ken_dem (sample data for this tutorial) [caption id="attachment_187" align="aligncenter" width="640"] Load DEM in QGIS[/caption]   Go to Raster > Extraction > Clipper (This will help us in…
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Using Free GPS Tools for Mapping

Using Free GPS Tools for Mapping

GIS
Sometimes we find ourselves lost while travelling. Right? But have you really tried to leverage some of the modern technology on your mobile phones to avoid trouble while navigating? Thanks to technology as of now, some of the things we wished for before are a reality. We can utilize powerful mapping apps effectively and for free over various platforms such as Android OS. Over the weekend, I travelled from the Nairobi (Capital) to the far West of Kenya. As I planned for this journey, I decided to use GPS Essentials (OpenStreetMap-Based navigation app for Android) on my Samsung mobile Phone to track my travel way. GPS Essentials offered a very good interface with many tools for use such as the Compass, Portable maps, Google Maps, Camera, Satellite viewer and many…
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Maps for the Color blind

GIS, QGIS, Software
We are living in an era of digital maps.We've evolved from static maps to dynamic maps where different formats(icons,pictures) of information are being developed and shared by a large group of people globally.When mapping,less often do we consider the color blind.How do you paint a picture or develop a map when the color blind is waiting to see the results.Over a long period, this has been a difficult area to tackle but thanks to QGIS.QGIS introduced the "Preview Mode" (Simulate Color Blindness (Protanope/Deuteranope)) which help GIS Analysts to create maps that will be perceived by all. To Do: In QGIS 2.4 (Windows) Go to "VIEW" > Preview Mode > (select either Simulate Color Blindness Protanope / Deuteranope ) The outputs for various modes have the visual difference as the images…
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Generating DEMS from Contours in QGIS

Generating DEMS from Contours in QGIS

GIS, Tutorials
Well, Today was a great day in my GIS works. A colleague asked “Can I generate a DEM of my region using QGIS?” This was my answer to them “YES”. Then they asked me “How?” I ended up spending the next one hour doing the demo on my laptop for them to grasp the rough idea on how to go about this issue. That question motivated me to write this post so as to help other persons/groups out there who might be stuck in this issue like my good friend. Here are the steps for generating a DEM (Digital Elevation Model) from CONTOURS using GRASS Plugin in QGIS. To start, ensure you have the GRASS plugin installed in your QGIS (Plugins > Manage and Install plugins >GRASS) Load the “Contours” …
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9 essential GIS skills

9 essential GIS skills

General, GIS
A GIS automates creating, analyzing, manipulating, storing , querying and retrieval of spatial data for users. However, there are various essential skills that a user should have to utilize the capabilities of a GIS with ease and produce quality products within the stipulated period of time and cost. GIS Data management          Data management is important to ensure that all data being used is put in an easily accessible location within the application to save time of retrieval.A GIS offers various data management tools to work with during analysis based on the data loaded in the application.The kind of projection used for data in a GIS is vital in determining the actual location of features on the earth’s surface.There are many projections available in GIS that can be used depending…
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Adding layers from GeoServer in QGIS

Adding layers from GeoServer in QGIS

GeoServer, GIS, QGIS, Software, Web-GIS
In a GIS, the ability to handle more data formats is of key priority while developing the system. This gives the GIS users a wider variety of formats to choose from during their analysis. QGIS has implemented this by allowing users to add data from many sources and in many formats. Loading a WMS, WFS or a WCS is one of the vital abilities for users carrying out web mapping operations with their data. The three formats of data can be loaded easily directly from GeoServer into QGIS. First we need to establish a secure connection between QGIS and GeoServer. Load the WMS/WMTS dialog window at Layers >> Add WMS/WMTS Layer on the Menu (QGIS) or by selecting the Add WMS/WMTS layer from the Manage layers toolbar. Select “New” to…
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Publishing maps using QGIS Cloud

Publishing maps using QGIS Cloud

GIS, QGIS, QGIS Cloud, Software, Tutorials, Web-GIS
Sharing the outputs of your GIS work with other people on the globe has become a common practice nowadays. The methods used in sharing this information matters and depends on a number of things;the availability of storage space to store your datasets, the cost of operating a web map,user interactivity of your web maps,the kind of technology the web map uses and many more. QGIS have the QGISCloud that is can be used to publish maps online within FIVE minutes.Another advantage is that QGIS is Open Source thus no worry of startup costs.This tutorial will demostrate how to publish a map using QGISCloud. Steps To publish a map using QGISCloud, you need to first install the QGISCloud Plugin.This can be done at “Manage and Install plugins” under the Plugins Menu…
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Adding data into ExtJS grid from PostgreSQL with PHP-The JSON format

GIS
Data loading from a database into an application is useful more so if there will be frequent changes on the data stored in the databases. The data is loaded from the database when the application is loading. Any changes on the data are reflected into the grid carrying our data in the application. I will demonstrate using PHP and ExtJS on how to query a database and return the data into a JSON format that will be used in our JavaScript application. First, we write a script that will query our database in PHP (data.php)  //data.php $db = pg_connect("host=somehost port=someport dbname=**** user=**** password=****") or die('could not connect:'.pg_last_error()); $result = pg_query($db, "SELECT *,ST_AsGeoJSON(geom) FROM Africa") or die("Data load failed:".pg_last_error()); $rows = array(          'type'      => 'FeatureCollection',         'features'  => array()  …
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