# Digital Geography

## D3: My First Webmap

I always watched those stunning examples created with D3 by Mike Bostock, I liked Ralf’s blog posts here and I always thought to myself: get yourself together and create one for your own. But to say it straight: I haven’t figured it out… But yesterday I stumbled upon this nice, not so short post of MappingGIS.com and I would like to share my learning process here. So let’s start …

## Python in QGIS and ArcGIS: A Small Example

Often the usage of GIS never touches the world of programming and I think a lot of GIS users today feel fine with using simple tools and try to avoid tools like Python for their daily work. Despite any prejudices regarding programming, Python can be a big help in your basic tasks and is a very easy scripting language to learn. So let us check out Python in ArcGIS and QGIS with a buffer analysis as an easy example. Nevertheless I recommend to take some coding lessons in Python using CodeAcademy.

## geoJSON with QGIS and leaflet: from data to map

The new JSON Format GeoJSON allows you to easily embed geographical features in your leaflet webmap. Additionally you can create it very easily in the open source GIS QGIS aka Quantum GIS. In this tutorial I’ll show you how to export features to GeoJSON from QGIS and embed them into your leaflet map.

## NDVI / SAVI calculation using Landsat scenes: DNs vs reflectance values

In one of my last seminars relating remote sensing techniques I was blamed for calculationg the NDVI and SAVI directly with the ModelMaker in Erdas Imagine using digital numbers (so-called DNs) instead of reflectance values. So I analyzed the influence of using DNs instead of reflectances. You can see some little thoughts and results on that here…

## Possible application for topologies

Most of my students asked me: “why do we need this or that!?”. In fact: for topologies I failed in answering often. One possibility of usage is shown here: In fact I was confronted with this problem more then once: two neighbouring polygons, move one, move the other and hope that snapping will do the rest. Using the topology tools in ArcGIS makes this much easier as it treats your shared vertexes as one vertex and adjust the geometry of both polygons… “Thumbs Up!” for that! Find more informations on topology here: LINK

## projections, ellipsoids/spheroids, coordinate systems, datum and all this crazy cartographic stuff.

We will go straight to the main part of the problem:how to communicate, where you are. Sometimes it is as easy as “one, two, three” but most likely it is as you are talking in another language compared to your listener. Let us assume you say something like “I am in the mall 500m northwest of the church”. Well there is plenty of information in it. More after the break!