Introduction
What is GIS?
GIS, Geographic Information Systems, can be simply described as “the use of computers to make maps,” but there is much more to it than that. GIS did get started that way, as an improvement to creating maps by hand. Storing the data in a computer allowed for quick modification of small parts of the map, without having to redraw the entire thing. Out of this beginning evolved the concept of sorting spatial information into themes of related topics (roads, rivers, buildings etc). These themes could be be overlayed on top of one another, just as used to be done with mylar sheets. A database full of interchangeable map layers which can be turned on and off at will can be used to produce a map on any topic. And, there’s more to it than meets the eye, because the graphical information shown on the screen (the points, lines and polygons) is linked to tabular data behind the scenes which holds additional information about each feature.
This tabular background data allows for more than just information display, and brings us into the world of information analysis. Using computer models and number crunching, GIS can be used to answer questions such as “find the number of restaurants within 5 miles of X” or “compute the total area of evergreen forest in this region” or even “figure out the fastest route from A to B” or “the best place to build our new business location given factors such as distances from other businesses of the same type and proximity to a certain demographic.” GIS software packages have built in tools for both of these aspects of GIS: the map making and the spatial analysis.
What does a GIS Analyst do?
The short answer to this one is, “A GIS Analyst knows how to operate GIS software,” such as ESRI’s ArcGIS, MapInfo or Intergraph. The range of tasks a company may want the analyst to accomplish with this software includes:
- Map production: selecting layers, choosing symbols for features, placing labels and legends and publishing as a paper printout, computer graphic, or web service.
- Data creation: Collecting spatial information from various sources and converting it into GIS layers. The two most common ways of doing this are through digitization and georeferencing.
- Digitization: The creation of a spatial dataset from a hardcopy source such as a paper map or aerial photograph. Usually done by scanning the map, georeferencing it (see below), then tracing the features on screen.
- Georeferencing: Assigning geographic coordinates (latitudes & longitudes, or some other coordinate system) to spatial data. This is done by aligning the data with a source whose coordinates are known.
- Database management: Adding attributes to data. (Attributes are the associated tabular behind-the-scenes information I mentioned above.) Organizing features into themes. Writing metadata that documents data sources, creation dates, processing history, etc.
- Automation: some scripting such as VBA, python or model builder to increase efficiency at repetitive tasks
- Data analysis: Answering those questions that a GIS can, questions about where things are located, the distances between them, the areas covered by them, the patterns and statistics seen in their spatial distribution.
This blog is written for GIS Analysts who have a basic familiarity with the ESRI ArcGIS software, and would like to get better at using it to accomplish the kinds of tasks I have described above. I will be sharing tips and tricks I have learned from years of working at engineering firms and facing real-life scenarios that are never as cut and dry as classroom assignments. I wish I had known these things starting out. They have made my life much easier!