Copyright © 2006 by Maribeth H. Price 1-1 How does GIS work? Data storage The ArcGIS Interface

Copyright © 2006 by Maribeth H. Price 1-2 Vector model Vertices Polygon Points Nodes Line X Y Features are stored as a series of x-y coordinates in a rectangular coordinate system. Many different coordinate systems may be used.

Copyright © 2006 by Maribeth H. Price 1-3 Features linked to data Each feature is linked to an entry in a data table containing information about the feature.

Copyright © 2006 by Maribeth H. Price 1-4 Advantages of vectors Precise location of features Storing many attributes Flexible for cartography Compact storage of information Ideally suited for certain types of analysis, especially areas, lengths, connections

Copyright © 2006 by Maribeth H. Price 1-5 The raster data model Rows Columns X, Y location Raster data file N rows by M columns X, Y location Georeferenced to earth’s surface

Copyright © 2006 by Maribeth H. Price 1-6 GIS data models Vector model Raster model

Digital Raster Graphic

Converting Vector to Raster Data is Easy

Converting Raster Data to Vector is Hard Impossible

Copyright © 2006 by Maribeth H. Price 1-10 Types of raster data Discrete raster: land use Continuous raster: DEM Continuous raster: image Discrete raster: roads

Some Common Image Formats JPG – Used for most digital photos but “lossy.” GIF – Best for line drawings. 256 colors maximum. No loss TIF – Standard in many technical applications. No loss PNG – Lossless image format RAW – Data as captured by digital camera

Copyright © 2006 by Maribeth H. Price 1-12 Continuous data Raster is the best way to store continuously changing values such as elevation Analysis faster and more flexible than vectors for many applications Some analysis only possible using rasters

Copyright © 2006 by Maribeth H. Price 1-13 Raster analysis functions Density Least cost path DistanceInterpolation Viewshed Buffers

Copyright © 2006 by Maribeth H. Price 1-14 Impact of resolution Storage space increases by the square of the resolution Portraying large areas at high precision is problematic 90m resolution 10m resolution

Copyright © 2006 by Maribeth H. Price 1-15 Storage of attributes Roads may have other attributes: ownership, speed limit, number of lanes, etc. Would need a new raster for each attribute Only numeric attributes may be stored Raster contains 1 value indicating a single attribute— road type for example

Copyright © 2006 by Maribeth H. Price 1-16 The raster data model Rows Columns X, Y location Raster data file N rows by M columns X, Y location Georeferenced to earth’s surface

Copyright © 2006 by Maribeth H. Price 1-17

Copyright © 2006 by Maribeth H. Price 1-18 ModelBuilder Create models built from sequences of tools Store processing steps for later reference Execute models repeatedly with different inputs Share models with others

Copyright © 2006 by Maribeth H. Price 1-19 Moonlight Bay Basin.shp Discard out-of-boundary spot elevations Export to delimited text Extract spot elevations every 50’ for 11 input datasets Merge 11 datasets bh_c.shp Contour2- point_bhc.shp Township 2-Foot Contours THE RIDGES SANCTUARY WATERSHED STUDY Geospatial Analysis - Summary Flow Diagram Revision Date: 10 September, 2007 By: Mike Stiefvater Boundary Of Area To Be Modeled WS0607- Boundary.shp Final Spot Elevations In x,y,c Format Input01.txt Thinned And Combined Township Spot Elevations Hydrologic modeling furnished by Door County Soil and Water Conservation Department Document Location of Known Outlets WS0607-outlet 4model.shp Calculated Subwatershed Boundaries South Outlet* Basin.shp Calculated Flow Paths Flow path.shp “Thinned” Elevation Data Contour2- point_all.shp Final Spot Elevations Contour2- point_clip.shp WS0607- Culvert.shp Hwy 57 Basin.shp Mud Lake Basins.shp Analytical Operation/ GeoprocessingTool Dataset * aka “Hidden Brook Subwatershed”