Exercise 3: Raster data analysis Course: Rakennetun ympäristön paikkatiedot RYM C2004 Date:

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1 Exercise 3: Raster data analysis Course: Rakennetun ympäristön paikkatiedot RYM C2004 Date: Introduction In this exercise we will analyze SLICES raster dataset that contains data about land use, land cover, soil types and special use and restricted areas. In this exercise you will work with the raster file and get familiar with basic raster processing, analysis, and representation tools and techniques in ArcMap. In its simplest form, a raster consists of a matrix of cells (or pixels) organized into rows and columns (or a grid) where each cell contains a value representing some information (read more at e.g. Esri website). Data stored in a raster format can be either thematic (e.g. soil types) or continuous (e.g. temperature, elevation, etc.). Johdanto Tässä tehtävässä analysoimme SLICES rasteri pohjaista tiedostoa, joka sisältää tietoa muun muassa maankäytöstä, maanpeitteestä ja maaperästä. Tässä tehtävässä työskennellään rasteridatan parissa ja tutustutaan tavallisimpiin rasteridatan käsittely, analyysi ja esittämistyökaluihin sekä tekniikkoihin. Yksinkertainen rasteri tiedosto koostuu vaaka sekä pystysuoraan järjestäytyneistä soluista (myös pikseli tai hila alkio) muodostuvasta matriisista. Kuhunkin soluun liittyy arvoja, jotka edustavat jotain informaatiota. Rasteridatan sisältämä informaatio on joko temaattista (esim. maankäytön tyyppi) tai jatkuvaa (esim. lämpötila, maanpinnankorkeus). Picture from Esri s website. 1

2 Where to find ArcMap ArcMap can be found from Maari B, Maari E and Maari K in Maarintalo, Y338 in the main building and K345 in Konetekniikka 1. Aalto University students can install ArcGIS Desktop to their personal computers from download.aalto.fi There are also trial versions of the software available on ESRI website. Learning objectives Recognize a raster file Use a basic raster processing tool (Clip) Learn how to Reclassify raster values Getting familiar with raster presentation techniques See a raster file s attributes table and use Statistics. Perform a simple raster analysis. Oppimistavoitteet Tunnistetaan rasteridata Käytetään rasteridatan prosessiointityökalua (Clip) Opitaan, kuinka rasterin arvoja voidaan uudelleen luokitella Opetellaan rasteridatan esittämisen tekniikoita Tarkastellaan rasteridatan attribuuttitaulukkoa ja käytetään Statistics työkalua Tehdään yksinkertainen rasterianalyysi Short instructions In this exercise we will first import a raster file to the ArcMap environment. The raster includes a very large area but we are only interested in a certain area around Helsinki metropolitan area, therefore we use the Clip tool to leave out the other areas. The original raster has many soil and land use classes, we want to simplify the map by having only 6 classes. Thus we generalize the classes into bigger ones. Then we will customize our map by changing the visualization (colors assigned to each class in the map). At the end we will do a simple math to find out what percentage of the total area is covered by the Forest class. 1. Import raster to ArcMap 2. Clip raster to the desired extent using Clip tool 3. Reclassify raster values into 6 classes, using Reclassify tool 4. Visualize the raster 5. Identify the percentage of land area covered by forests. 2

3 Short instructions Tässä tehtävässä tuodaan ensin rasteridata ArcMap:in. Käyttämämme raster on todella iso ja olemme kiinnostuneita ainostaan tietystä alueesta sen sisällä, joten käytämme Clip työkalua saadaksemme vain tietyn osan rasterista käyttöömme. Alkuperäisessä rasterissa on monia maaperä ja maankäyttöluokkia, mutta haluamme luoda yksinkertaistetumman kartan ainoastaan kuudella luokalla, joten tavoitteenamme on yleistää ja näin siis yhdistää luokkia. Tämän jälkeen haluamme kustomoida karttaamme muokkaamalla sen visuaalista ilmettä (kullekin luokalle omat värit). Lopuksi teemme yksinkertaisen matemaattisen laskutoimituksen selvittääksemme, kuinka suuren osan Metsät luokka kattaa. 1. Tuo rasteri ArcMap:in 2. Clip työkalulla leikataan raster haluttuun kokoon 3. Uudelleen luokitellaan rasteri kuuteen luokka käyttämällä Reclassify työkalua 4. Visualisoidaan rasteri 5. Tunnistetaan, kuinka monta prosenttia maa alasta on metsien peittämää Detailed instructions Part A: Preparation Download the data Download the data from MyCourses. Unzip the files (right click > Extract All) in a folder of your choice in your Windows file system. Start ArcMap Start ArcMap from Start Menu > All Programs > ArcGIS > ArcMap Add the raster data Click on the Add Data button. Connect to the folder where you have saved the unzipped files. Open the file ul4_10f.tif. Investigate the data You must now see a map on your screen. Zoom to the layer and try the Identify tool. Try to select one of the cells using the Select features tool (Yes, you can t!). Part B: Data preparation Clip the raster file to the desired extent Open the Arc Toolbox panel. Go to Data Management Tools > Raster > Raster processing > Clip Clip the raster to the following extents. To make things easier, use the rectangle Shapefile provided to you in the dataset (Add data first). Name the output as rasterclip and leave the other options as default. 3

4 NOTE: If you cannot access the tool, check that the ArcGIS extensions are activated for you. To do so, in the top bar navigate to Customize > Extensions. Make sure that there is a tick next to all extension names in the list. Part C: Reclassification In the SLICES dataset there are almost 50 land use classes. In this exercise we will reclassify the raster to 5 classes, leaving the rest as Other. Current classes New classes 11 (Economical buildings) 5 (Buildings) 44 (Public buildings) 14 (Residential buildings) 62 (Roads) 4 (roads) 65 (Railway and tracks) 220 (Sea) 3 (Sea) 202 (Unregulated waters) 2 (Lakes) 203 (regulated waters) 92 (Meadows) 1 (Forests) 121 (Woodland) 122 (Scrubland) Other values 6 (Other) Reclassify raster values according to the table above Go to Spatial Analyst Tools > Reclass > Reclassify. Choose rasterclip as the input raster and choose value as the Reclass field. Click on Unique and assign new values in the Reclassification table according to the table above. NOTE: in order not to confuse new values with the already existing ones, instead of using 1, 2,5, use values 1001, 1002, 1005 as new values (Table below). Name the output as rcls1 and click OK. 4

5 OLD VALUE NEW VALUE 11, 44, , , , 121, OTHER VALUES Leave them as they are Once again open the Reclassify tool (Spatial Analyst Tools > Reclass > Reclassify). This time we want to reclassify values from 1000s to the desired 1, 2, 3, 4, 5 values and assign 6 to other existing values. Choose rcls1 as the input raster and make sure that Value is chosen as the Reclass field. Click on Classify button. Choose 6 as the number of classes and change break values to 1000, 1001, 1002, 1003, 1004, This will reclassify all existing values (<1000) to one class and assign new values starting from 2 to other five classes. Click OK. Note: Arcmap can be a little stubborn when you are trying to manually edit break values. Don t give up! You can change them. In order to adjust class values to the desired format as presented in table above, reassign values so that your Reclassification table looks like this: Choose the output name as final and Click OK. Part C: Visualization Assign suitable colors to represent each class Find the raster called final in the Table Of Contents. Right click on it and choose Properties. Go to the Symbology tab and choose unique values. Assign an appropriate color to each class and click OK. You can choose whatever color you like but try to choose colors that are relevant to the class type. 5

6 Class value Class type Color 1 Forests Green 2 Lakes Light blue 3 Sea Dark blue 4 Roads Yellow 5 Buildings Purple 6 Other Grey Note: color customization can also be directly done from Table Of Contents. You can now add the desired map elements (title, legend, north arrow, scale bar) and export the final map. Note: Remember to add class names to the legend. You can do this by adding a label for each class in the Symbology window. Part D: A simple analysis What percentage of the total areas is classified as Forests? Right click on final raster in Table Of Contents and choose Open Attribute Table. Right click the Count field and select Statistics. Use the information provided in this window what percentage of the total area is covered by forests? Submitting the report Submit your report to the exercise s folder in MyCourses as a single PDF file. You can save your report to PDF format for example in Word or OpenOffice. A report written in English is preferable. Remember to name your file as LastnameFirstname_ExerciseN.pdf The report is graded from 0 5. You will get a 0 from the exercise if you do not submit your report before the deadline. For a grade 5 your report must include: A brief review of what you did in this exercise (feel free to include screenshots). The final map Answer to the following questions: 1) What is a raster data and how is it different from a vector? 2) In your final map, what percentage of the total areas is classified as Forests? (Part D) Report is due as informed in MyCourses. In case of questions contact: kamyar.hasanzadeh@aalto.fi 6

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