2 - Key Concepts
Tobbler’s First Law
Everything is related to everything else, but near things are more related than distant things.
This is one of the basic principle of GIS. We study locations, because we think they are some commonalities and/ or associations when things are proximate to each other.
What is GIS?
- GIS stands for Geographic Information Systems
- GIS allow you to analyze your data spatially; hence not merely a visualization tool, but a system that allows you perform spatial analyses.
- Five components of GIS
- Hardware, methods, people, data, and software
- GIS is a world of layers
- Static maps
- Interactive maps
- Both static and interactive maps
If you are new to GIS, I’d recommend starting from QGIS. QGIS is free and open source GIS software that is compatible with both Mac OS and Windows OS. QGIS’s functions have gotten better over the 10 years. Maybe in future, mapping could move to coding…? What do you guys think?
GIS techniques are commonly used in various fields from ecology to public health, urban planning, and resource management.
Below are examples of common GIS applications
- Data classification (examples)
- income map
- facility distribution map
- disease distribution map
- Simple geo-processing
- density calculations
- aggregation (use with caution) `
- Spatial analysis
- cluster analysis
- hot-spot analysis
- network analysis
- geographically weighted regression
Coordinate systems + projections
Since GIS is a world of layers and the Earth is not flat, geographic coordinate system is important to properly perform analysis.
- Geographic coordinate system
- “A geographic coordinate system (GCS) uses a three-dimensional spherical surface to define locations on the earth” (Esri)
- read more: https://desktop.arcgis.com/en/arcmap/10.3/guide-books/map-projections/about-geographic-coordinate-systems.htm
- Projected coordinate system
- “A projected coordinate system is defined on a flat, two-dimensional surface. Unlike a geographic coordinate system, a projected coordinate system has constant lengths, angles, and areas across the two dimensions” (Esri)
- read more: https://desktop.arcgis.com/en/arcmap/10.3/guide-books/map-projections/about-projected-coordinate-systems.htm
Two main data types of GIS - vector - Consists with lines, points, polygons - (e.g.) streets, trees, census tracts
- consists with pixels
- (e.g.) satellite imagery, results of kernel density/ interpolation
- file extensions
- .shp [shapefile - vector]
- comes with so many subfiles and often heavy, but do not delete subfiles!
- .csv [comma separated value - vector]
- often used for goverment data like census
- careful with data types, such as string or integer when loaded to QGIS: excel changes data types without telling us…
- .json [geojson - vector]
- .jpg [image - raster]
- . qgz or qgis [map file - QGIS]
- .mxd [map file - ArcGIS]
- .shp [shapefile - vector]
- Searching geodata
- Google: /what you are looking for/ shapefile
- (e.g.) nyc parks shapefile
Remember! Non shapefile data can nbe turned into a shapefile data by joining or geocoding!
When visualizing data on a map, following are most common symbols to use. Maps can magnify your results depending on how your present your results or how you classify them. Please be extra careful when you are visualizing. You do not want to give people false impression of your research results. Creation of an accurate map is important!
- GIS software let you classify your data:
- Equal intervals
- Standard Deviations
- Natural break (where your data clusters)
- Manual (you classify your own)
When you make a map, make sure to include the following elements:
- north arrow
- scale bar
- data source
Map design can be challenging, mainly becasue people will have a hard time selecting the most important information on a map. Make sure to remove all the elements you don’t need and do not make your map cluttered. Some elements to keep in mind when designing a map are:
- color use
- images attached to colors
- consider color use for color blind people
- visual hierarchy
- What is the most impotant element on your map?
- white space
- Do not pack your map with informaion. Give it a plenty of breathing space!