What is GIS? Geographic Information Systems Introduction to ArcGIS A database system in which the organizing principle is explicitly SPATIAL For CPSC 178 Visualization: Data, Pixels, and Ideas. What Can You Do With GIS? With GIS, you can analyze EVERY POSSIBLE MAP! With the right data, you can examine Land Elevation Population density Distance to public restrooms Noise levels GIS Maps Contain Layers GIS organizes the world into layers of geographic objects that are alike. Anything you can associate with a location! Layers Can Contain Features Features are geographic objects that can have shape and dimension. Can be modeled as points, lines, or polygons. Mine Locations Streets Census Blocks This is referred to as the Vector Data Model Features Can Have Attributes In this example, each Census Block feature is associated with dozens of Demographic Attributes 1
The Raster Data Model The Raster Data Model is used to model spatial phenomena that vary continuously over a Surface and that do not have discrete dimension Elevation Temperature Rainfall Noise Levels Things like elevation, temperature, slope and precipitation have measurable values for any particular location on the earth s surface. To model these phenomena, an area of interest is divided into an array of identically sized squares The centers of these squares then become the sample points The values of the variable of interest are recorded, or estimated, at each of the sample points. These values can then be assigned colors, or shades of gray, in order for them to be visualized The most familiar type of Raster Data is the digital photograph. Digital Photos are raster datasets that record the relative amount of light being reflected off of a surface. Digital Photos 2
Putting It All Together GIS Analysis Because GIS Data is organized based upon location, unlike data can be overlaid and analyzed based upon spatial relationships: Coincidence Proximity Containment Adjacency Intersection Suppose we are interested in the parts of streets that are within 500 meters of rivers & streams in a city using GIS Software, we can create a 500 meter buffer around all rivers & streams in our area of interest then we can overlay our streets with this new buffer feature and finally, we can clip the streets to extent of the buffer feature to end up with a layer that describes all streets within 500 meters of a river or stream! Or perhaps we would like to examine the statistical relationship between two variables. For example, elevation and temperature 3
We can overlay our elevation and temperature data, based upon location The values from each data layer can then be extracted for corresponding locations these values can then be exported to statistical software in order to examine whether there is a statistical relationship between elevation and temperature 4
ArcMap Window What is a Map Document? A Map Document is the file that you save you cartographic work in (data references, symbology, labeling, etc ) ArcGIS uses a proprietary *.mxd file format to save map documents. In many ways similar to a Word document (.doc) in that you can save, print, etc however What is a Map Document? It is a collection of references to objects (GIS data files) and properties of those objects All of the data that you add to a map document does NOT get stored in the map document. Only the reference to that data gets stored. Making a Map This means if you move the data, the map document won t know where it is! If you send someone a map document, they won t be able to read it unless you send the data as well Dot Density & Choropleth Maps high medium low 1 dot = 100 people use raw scores use density data e.g. Population e.g. Population per Square Mile Raw Count vs. Normalized Data in Choropleth Mapping Choropleth mapping using raw' count data can be deceptive. In the example below, some counties with very large areas appear to have been overrepresented in terms of population. Raw count data should be normalized using area to account for this overrepresentation. Dot Distribution Map Good for showing raw count data. Visually indicates relative density. Choropleth Map Good for showing in easily interpretable classes Easier to interpret with fewer color/shading patterns, usually 5-20 different classes Count data should be normalized 5
Essential Map Elements Title What is your map about? Should be the biggest text on the page Should be descriptive Feel free to use a sub-title in order to provide more information Location In the title Using Graticules With an inset map Scale Scale bar Representative fraction Or both Orientation North Arrow Stay simple Be careful about position Drawn for? Agency, class name Legend Key Put everything in the legend Projection List the projection your map is drawn in Sources Just like citing sources in a program Outline data sources, attribute data sources, image data sources Dates Dates on data sources Date map drawn Cartographer Put your name on the map Neatline Everything must be inside the neatline 6