Lab 4 Digitizing

Lab 4 Digitizing - 44:005 Foundations of GIS Lab 4 Creating...

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44:005 Foundations of GIS Lab 4: Creating Digital Spatial Data Spatial data can be generally defined as information relating to the location of, and relationships between, geographical features. In previous labs you have worked with preexisting spatial datasets. In this lab, you will explore two techniques for creating your own spatial datasets (in this case, shapefiles). Overview of the exercise… Overview of different vector and raster files used in ArcMap and ArcCatalog Creating a shapefile from a text file containing x,y coordinates Creating a shapefile using heads-up (on screen) digitizing Part I: Types of Spatial Data used in ArcMap and ArcCatalog In this lab you will be working with both raster and vector datasets. Recall from Chapter 2 and lecture that a vector file contains a collection of points, lines and polygons that represent a collection of real-world feature such as cities, buildings or lakes. A raster file, on the other hand, is composed of pixels and is used to represent some continuous surface such as elevation or air pollution. If you zoom in on a raster image, you will see that it is made up of tiny cells. Let’s look at some of the different vector and raster file types that can be used in ArcMap and ArcCatalog. 1. Copy the Lab4data folder to your student folder. 2. Open the Lab4data folder so you can see the files and select View Details so you can see the file types. 3. Start ArcCatalog and navigate to your Lab4data folder. You may need to connect to your Lab4 folder in order for it to show up in the TOC. Look at the files as they are listed in the ArcMap Contents tab. You can see that Lab6data contains some shapefiles , some raster files and one coverage file. Shapefiles Shapefiles are one type of vector file used in ArcMap and ArcCatalog. Recall from Lab 2 that My Computer and ArcCatalog show you two different views of the same files. “Shapefiles” are actually a collection of files. As long as they have identical names (prefixes), ArcCatalog and ArcMap recognize that they belong to the same “shapefile” and display them as a single file. That is why Jhns_roads_2000 is represented as seven distinct files through My Computer and only one file in ArcCatalog and ArcMap. 044:005 Lab 4 p.1
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A “shapefile" may be composed of six or seven different files. However, only three of these files are absolutely necessary: .shp , .shx and .dbf . At the bare minimum, the “shapefile” must contain these three files as they hold the shapes of the features, an index to all the features in the dataset, and the contents of the attribute table. (Wikipedia has a good overview of these file types.) Various raster files ArcMap supports many different raster file formats. You have already worked with .tif and .img files in previous labs. The Lab4data folder contains aerial photos, topo maps, digital elevation models (DEMs) and even a photograph of a panda bear! You can select each of these raster files in ArcCatalog and
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  • Fall '11
  • DavidBennett
  • Geographic coordinate system, Coordinate system, Raster graphics, Geographic information system, attribute table, Shapefile

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Lab 4 Digitizing - 44:005 Foundations of GIS Lab 4 Creating...

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