Downloading and Repairing Data

Transcription

1 Overview In this exercise you will find and download spatial data for the town of Lowville in Lewis County, New York. The general idea of the exercise has changed from one of simply downloading data and making a map to downloading, repairing the data, and making simple maps. You will download data from both the CUGIR site at Cornell and the USGS National Map. The National Map system can be frustrating but that is the name of the game in the real world. What gets turned in? A short description of problems you had in doing this exercise, Answers to the questions (on the answer sheet), and the final map shown at the end of the exercise. And, of course, the reflection page. Assignment CUGIR: Is an easy to use interface. 1) Type CUGIR into the URL space in your browser or use a search engine to find the site. 2) Click on the select by Map button. 3) Click on Lewis County. 4) Download the following layers and the metadata for each. MAKE NOTE OF THE FILE NAMES. a) Ag Districts in ArcExport form. b) County Boundary for Lewis County. c) Minor Civil Divisions for Lewis County. d) Lowville 1:24,000 quad digital raster graphic. 5) There are several different forms of data here. The digital raster graphic is a GeoTiff image of the quad sheet and is pretty easy to handle. The Ag Districts layer is in ArcExport form that has been Gnu zipped but FilZip can handle that ok. Use ArgGIS help to find out how to convert the ArcExport data to a Coverage. (Hint: it is in the tool box). NOTE: COVERAGE IS A FILE FOLDER. DO NOT TAKE ANY FILES OUT OF IT! National Map: The national map interface is a national seamless database, or really access to seamless databases from many agencies, from which you can download all kinds of data. Any professional using GIS should know about this rapidly improving access to quality data well, usually quality data sometimes useful metadata is missing! And the system is complex and requires that you understand extents and longitude/latitude coordinates. 1) Get to the National Map by typing National Map in the URL space in your browser or by using Google or some other search engine. You want the national map at USGS. The opening window should look like the window at the right. C:\Websites\lpherrin\557\Exercises\PM3a.doc 9/29/2004 Page 1 of 7

2 2) If you have never used the National Map click on Viewer Help. Doing so will reduce some of the frustration of using this system. 3) Click on Viewer. 4) Drag one side or the other of the viewer window so the mapping area is roughly square. 5) A map of the US&A should be displayed. a) Use the zoom tool (tool bar on the left) to zoom in to the area just to the NE of Syracuse. As you zoom in additional layers will be added to the display. Just like ArcGIS you can click on the map for a fixed zoom or you can draw a box. b) At some point turn on the LandUse/LandCover layer 004_EVI_2003_305 so that your display looks like mine (image to the right). c) Find the roads intersections shown to the right. The coordinates (approximate) of Lowville are -75 o 29 12, 43 o d) As you get zoomed in check that the roads layer (USGS only), the LandUse/LandCover, and the shaded relief layers are turned on. These are the layers you are going to download. 6) Your map should look something like that shown below. Your extent does not have to be exactly the same as mine. 7) You may have to mess with the screen size and the amount of zoom to get what is shown. 8) Click the download tool. A Window appears that lists the layers to be downloaded: a) US NED Shaded Relief b) 004_EVI_2003_305 c) Roads BTS 9) Click Download Data. 10) Now you get the Archives of Extracted Data window. This window has links to the download sites for the data. And I have cleverly picked three layers that have different download processes. Oh Joy! 11) MAKE NOTE OF THE MAX AND MIN X, AND Y! You will need them later (note, they are the same for all the layers). 12) Click on the first link. You will get a save dialog; save the data in your workspace. 13) Click on the second layer (EVI layer). Now you get a different download facility that starts with another window like that for the National Map. C:\Websites\lpherrin\557\Exercises\PM3a.doc 9/29/2004 Page 2 of 7

3 Agh! Do I have to do all that zooming again! NO! 14) Scroll down to the downloads tools and select the tool for Define area by coordinates. 15) A dialog appears that asks for the extent of your data in Longitude, Latitude. You did write down those coordinates, right? Click on Switch to Decimal Degrees link. 16) Enter in the bounding coordinates in the right place. (Actually, the window with the coordinates should still be open and if it is you can copy and past the values into this dialog) NOTE THAT THE COORDINATES USE THE NOTATION OF N, S, E, AND W SO DO NOT ENTER ANY OR + SIGNS! A Dialog will tell you if you get values backwards when you 17) When done click Add Area. 18) You get a dialog called SDDS Request Summary Page Look at it and click Download and save the data. Make note of what it is because it will have a nonsense (to you) number for a name. 19) Now download the last layer. It will be a little different but similar to the above. Learn by trial by fire! 20) Now you have the data so unzip it with Filzip or Winzip. Just double click them. 21) The data is in different formats. 2 are raster files of different types and 1 is a good old shape file. DO NOT UNDER ANY CIRCUMSTANCES REMOVE ANY FILES FROM FOLDERS THAT CONTAIN AN INFO FILE! If you do you will destroy the data. You have to move the entire folder in windows explorer OR, better yet, use ArcCatalog to move the folders. 22) Open ArcCatalog. Your workspace should look like the image at the right. Using the notes you made when downloading change the data names to something more useful. 23) Look at the metadata for the grids and the road shape file. Preview the data. The METADATA.shp is strange I don t know what it is. The globe icon is the.prj file for that file. (Metadata is accessible via a link at the lower left of the National Map dialog. The Problem Now add the data to a map document. But there are two problems with the data that you will have to deal with before you can continue. Both of the problems have to be fixed with workarounds. Where did the work-arounds come from? Through my messing with the data and from talking to other ArcGIS 9 users (Mark Storings in the MSL in particular). 1) Open ArcMap and: a) Add the roads layer from the national map. b) Add the GeoTiff o4584b.tif part of the quad sheet. 2) Q1: Can you see both the roads and the GeoTiff? 3) If you can then you are home free. 4) If not then you have a problem. Here is the work-around for this problem. a) Open a new blank document. b) If you didn t download the metadata for the GeoTiff then either do so or look at it. i) Q2: What is the coordinate system? C:\Websites\lpherrin\557\Exercises\PM3a.doc 9/29/2004 Page 3 of 7

4 ii) Q3: What is the datum c) IF YOU DIDN T WRITE THEM DOWN IN THE SPACE PROVIDED DO SO NOW! d) Add the GeoTiff e) Open the DataFrame s properties and pick the general tab f) The current coordinate system window does not have much useful info, if any. g) Select the predefined coordinate system that matches what you wrote above h) Finish the definition process (You have done this before, believe it or not). i) Ah! Q4: That looks better, right? j) Turn off everything but the two roads layers k) Do the common roads match spatially? How well? l) Keep zooming in until they don t match. Q5: What is the approx. error? meters. m) Is that good or what! 5) Turn off the roads layer that shows only the main roads and turn on the GeoTiff. 6) How well do the roads match the image of the quad sheet? 7) Q6: Is the error an offset (everything shifted in some direction the same amount) or is it more or less random? 8) Now add the road layer. It should show up overlain (probably partially) on the GeoTiff. If not, you did something incorrectly go back and try again. a) Open the attribute table of the road layer. Oops! ArcGIS does NOT like that and opens an empty table. I downloaded this file three times and I never got a layer that was not corrupt. If you have a table then skip to step 9; If not, a work-around follows. i) Remove Roads. ii) Open ArcView 3.3. Something new! iii) Click OK on the first two dialogs that appear: a) open a new project Make sure With a new View is selected, and then b) Would you like to add data to the view now : Click Yes. iv) You now get the Add theme (same as layer in ArcGIS) dialog. Make sure the Data Source Type window in the lower left is set to Feature Data Source. Browse to where your corrupted roads data is stored and open the shape. The data will be added to View 1. v) The roads file is listed in the TOC and should be turned on AND active. In ArcView 3x active means the panel in the TOC appears raised from the TOC panel. See graphic to right. vi) Now click on the Open Attribute table button located just below the Theme menu choice. vii) There should be data in the table that opens. Don t ask me why AV3.3 can open this and ArcView 9 cannot! viii) Close the table ix) Now for the fix. (1) In the Theme menu select Convert to shapefile. (2) A dialog opens that looks like the usual find file dialog but has a few booby traps of its own. (READ (3) AND (4) BELOW BEFORE DOING ANYTHING ELSE!). C:\Websites\lpherrin\557\Exercises\PM3a.doc 9/29/2004 Page 4 of 7

5 (3) Browse to folder where you have your data stored. (4) NOW enter the new file a name (If you name the file first, which is the natural tendency, as soon as you browse somewhere it will be changed back to Theme#.shp. You won t notice this and wonder where your file went! (5) Exit ArcView 3.3 (In the File menu). b) Now go to ArcView 9 and add the new roads file. The table should now be available. 9) Add the rest of the data. 10) Some of the layers have larger extents than others and are awkward to work with so we are going to clip a couple of them. This is an introduction to the tool box. Here are the steps a) Open the file that is the towns (minor civil divisions) within Lewis County. See the figure to the right. b) Use the Select by Attribute process to select the town of Lowville (shown in green outline to the right). c) When it is selected Right click the layer name, Click on Data and select Data and then Export. The dialog below appears. X d) Make sure your looks like the above except for the data. location. Click OK. e) This makes a new shape of just the town of Lowville. You will be asked if you want to add it to the current map. The answer is yes. 11) Here is the procedure for clipping. a) Add the Toolbox to ArcGIS by clicking on the red toolbox. b) Click on Analysis tools, Extract, and then Clip. c) Double on the Clip tool hammer. d) The Clip tool dialog opens. i) In the first window browse to the file to be clipped in this case the roads that works (removed the old one, right?). ii) So select roads iii) The second window is where the clipping file (cookie cutter) is added and that is the Lowville file you just made. iv) In the bottom window make sure the path is to where you store your data and that you have given the new file resulting from the clip a useful name (the default probably is not bad). v) Click OK and the new data is added to the TOC. e) Now do the same thing to the Ag Districts file. C:\Websites\lpherrin\557\Exercises\PM3a.doc 9/29/2004 Page 5 of 7

6 12) As Proof of your pudding produce two maps similar to those shown below. Yours will not be exactly the same since It is unlikely that you used the same extent when you downloaded the National Map Data. 13) C:\Websites\lpherrin\557\Exercises\PM3a.doc 9/29/2004 Page 6 of 7

7 M3b Answer sheet this is included in report Q1: Can you see both the roads and the GeoTiff? Q2: What is the coordinate system? Q3: What is the datum Q4: That looks better, right? Q5: What is the approx. error? meters. Q6: Is the error an offset (everything shifted in some direction the same amount) or is it more or less random? PLEASE NAME AND ASSIGNMENT, IN THIS CASE M3A, ON THE BACK OF THE LAST SHEET OF THE PACKAGE C:\Websites\lpherrin\557\Exercises\PM3a.doc 9/29/2004 Page 7 of 7