Exercise 3: Building a GIS data library

Transcription

1 The Scenario You are preparing for an interview for a GIS position for a particular county. They asked that you present a GIS demonstration as part of your interviewing process. You decide to develop a GIS demonstration using local data. You need to find and download data for the county where you will be interviewing. Exercise 3: Building a GIS data library The world of GIS is expanding everywhere. With this expansion, access to quality GIS data is also expanding. Many countries, states, counties and even cities have GIS data available for public use. In many cases, this data can be downloaded directly from web sites or FTP servers. Although this data is freely available in most cases, downloading, converting and, eventually using this data can pose some challenges. In this exercise you will collect GIS data from the internet and process that data so that it is in a GIS-useful format. In this exercise you will: Find, download and convert GIS data Learn more about spatial extent and projections learn more about organizing your data

2 Data management tips Below are a few tips to consider when downloading and storing GIS data. It is wise to always document the source of your GIS data. Depending on how you will use the data you may need to acquire permission to use the data or, at the very least, acknowledge credit to the data provider. Whenever you need to move, modify or rename your GIS data, you should do so in ArcCatalog. Attempting this is Windows Explorer could damage your data. You may want to store your data based on project, or you may wish to store your data based on location. In either case, avoid multiple copies of the same data. As you begin to make modifications, you might find it a challenge to distinguish which file you are using. The same is true for multiple copies of a similar ArcMap document. Once you have downloaded compressed data and have converted or extracted it, you may wish to delete the compressed, downloaded file. This will save you data storage space. Page 2

3 Finding additional GIS data sources 1. Choose a county for which you want to create a GIS data collection. 2. Search that county name, as well as the term GIS data in an internet search engine. 3. Investigate the available links. Many counties have GIS data available through their web sites. However, you might find that there is limited GIS data available for your county of choice. Some counties do not provide online GIS data. Some counties have not yet implemented GIS. You may need to choose a different county to focus on. 4. When you have found the source of downloadable GIS data, evaluate the available data and download what you see as appropriate. You might have the inclination to download everything they have available. Bear in mind that you will need to store all of the data you download, so be sure you have sufficient data storage capacity. 5. Record the sources of the GIS data you download, including the layer name, the web site and the date you downloaded the file. 6. Once you have downloaded the county-level data, use the steps in Appendix A: Data conversion to extract the data to a format that is ArcGIS compatible. You may also wish to search for data at a different spatial extent, including the state, any large cities within the county or any state or national parks within the county. 2 Some counties do not make their GIS data available for free from the internet. 4 This is an example of an File Transfer Protocol (FTP) internet site developed to distribute GIS data. Page 3

4 Clipping data based on the outline of another layer (cookie cutter) For this task, you will use the Analysis Tools/Clip tool found in ArcToolbox. 1. Open ArcToolbox from either ArcCatalog or ArcToolbox. 2. Navigate to Analysis Tools / Extract in the ArcToolbox catalog tree. 3. Open the Clip tool in the Clip tool in the Extract toolset. 4. Specify the data set you wish to clip in the Input Features A bit about ArcToolbox ArcToolbox is organized based on Tool Boxes and Tool Sets. Each tool set contains additional tool sets or tools related in fucntionality. ArcToolbox can be opened in ArcMap or in ArcCatalog. When using ArcToolbox with ArcMap, you can select the input data from a drop down list of layers in teh ArcMap document. ArcToolbox tools have several commonalities. Each required field has a green circle near it. If the specified field value you entered is incompatable, the circle will turn red. Also, each tool has a help window, accessable via the Hide/Show Help button at the botton of the tool dialog. General help information will appear when the tool is opened or if you click the background of the tool. Specific help will be provided for each field when you click that field. Page 4

5 field. 5. Specify the dataset you wish to use as the cookie cutter in the Clip Features field. 6. Specify the fiel path and name of the shapefile you will create in the Output Feature Class field. 7. Click OK to begin the geoprocessing function. A processing window will appear, providing details in an incomprehensable coded language of the tools progression. If red text appear, some setting did not function correctly and you will need to re-run the tool after correcting any errors Exercise 3: Building a GIS data library 7 Page 5

6 Creating a new shapefile from selected features 3 1. Add a feature class to an ArcMap document. 2. Select some or all of the features, using either the select tool, selection options on the Selection dropdown menu, or by slecting features in the attribute table. 3. Right-click the layer name in the Table of Contents. 4. Select Data from the content menu. 5. Select Export Data. This will open the Export Data dialog box 6. Leave Select Features as the Export option. 7. Specif y where you would like to export the new dataset. 8. Click OK Page 6