GIS concepts, skills and tools Midterm Review GIS concepts, skills and tools

A GIS is a tool for making and using spatial data Cartography Data Processing & Analysis

Functions Supported by GIS Software

Today’s Overview: Earth Model and Projections Cartography Spatial Analysis Software and File Structure

Modeling the Earth: Describing the Ellipsoid: • Flattening: f = (semimajor-semiminor) / semimajor • Value often given inversely: 1/f

Ellipsoids Approximate the Geoid Why an Ellipse still isn’t perfect… Earth’s Geoid

Add coordinates to ellipse to get a datum NAD83 NAD87 WGS84

Ways of Measuring Position on Earth

Geographic Coordinate System! Taking Spherical Coordinates and plotting them in X Y:

General Types of Projections These different methods of projection lead to different map perspectives and different areas of distortion

Example: Cylindrical Projections This projection is how the well-known (much to the disappointment of many) Mercator map is created. UTM maps are common!

Why are Projections in ArcGIS Important? Three Spatial Orientation Situations: data has no coordinate system – project data has mismatching coordiante system – reproject project “on the fly” - Projecting data creates a new feature class - Think about editing!

Cartography: Representing Data Well Symbology Color Ramps Examples for Point Features: Certain color ramps work with certain map types

Binning Data Where should the data be split? Possible Options: Manual Natural Breaks Equal Interval http://resources.arcgis.com/en/help/main/10.1/ search “Data Classification”

Elements of a good map: The 5 Ds: DOGSTAILS Design, Density, Description, Distance, Direction DOGSTAILS D Date When the map was made O Orientation Directions (north arrow) G Grid Locates places on the map S Scale What the map distance is T Title What, where, and when A Author Who made the map I Index Map address of places L Legend What the symbols mean S Sources Basis for map information

Spatial Analysis - Spatial Data Model GIS is a simplified version of reality Definition: Objects in a spatial database plus the relationships between them

In GIS, data holds the answers to: Where? Location of features What? Properties and attributes of features

Main data model types Calculations Spatial selection Imagery … Spatial selection Cartography …

The Roles of Raster v. Vector Data

Different data examples we’ve used:

Skill List Selection & Geoprocessing Raster manipulations – reclassification, calculations, etc. DEM modeling – slope, flow, etc. Statistics Interpolation Editing - Hand digitizing, attribute data entry Georeferencing Clear Symbolization Conversion – moving data between formats

Common Geoprocessing Operations Querying Example of a spatial operation: SQL language: Selecting data subsets Spatial Operations Buffer Clip Intersect Union Merge Dissolve

Raster Calculations Math Conditional Statements Reclassification

Using rasters for analysis… Zonal Statisitics

Flow Direction on a Raster: The Hydrology Toolbox let us model flow in the Boulder Creek watershed

Editing How we change data: Projections Vector data editing Geoprocessing Hand digitizing Attribute table Raster adjustments Calculations Classification Deletion of classes Resampling

Georeferencing World Files Create one … Export one…

We use different Arc software for different functions Software Structure File and data management Interactive space Cartography and spatial processing 3D visuals We use different Arc software for different functions

ArcGIS Toolbox – what we’ve used (via the red box interface) Buffer Clip Intersect Union Merge Dissolve Geoprocessing menu

ArcGIS Toolbox – More of what we’ve used

Shapefiles <> File Geodatabase spatial index format (.sbx) attribute format (.dbf) projection format (.prj) spatial index format (.sbn) shape format (.shp) shape index format (.shx) geospatial metadata (.xml) Sometimes writing to a Geodatabase works better!