PrintNow that you've finished designing your map, you're ready to start creating the cache of map tiles. As an advance notice, you should plan at least one continuous hour to work on this page of the lesson.
In this lesson, you'll learn how to create tiles using ArcGIS Server. However, tiles can be created using many other types of GIS and mapping utilities. Mapnik is an example, which is used to create the tiles for OpenStreetMap.
Map tiling has become so popular that the Open Geospatial Consortium (OGC) has even released the Web Map Tiling Standard (WMTS) detailing an open specification on how mapping web services should expose their tile sets. ArcGIS Server services that have a tile cache can respond to WMTS-formatted requests.
Creating a tile cache with ArcGIS Server
When you publish a map service or image service in ArcGIS Server, you can define whether it will have a cache and what the cache properties will be. You can either build the tiles right at the time the service is published, or you can instigate the tile building later using geoprocessing tools like Manage Map Server Cache Tiles. Building the tiles at publish time is appropriate for smaller cache jobs, and that's what we'll do in this lesson.
- Make sure you are logged in to your EC2 instance and displaying your Little Rock project in ArcGIS Pro. In other words, you should be at the exact same point where you left off in the previous section of the lesson.
- Click Share - Web Layer - Publish Web Layer, and start the process of publishing a map service named LittleRock using the pattern from previous lessons.
- This time, in the Data and Layer Type section, click the radio button specifying the Tile option under Copy all Data.
- Before you publish this new service, click the Configuration tab and click the edit button next to the Tile layer. Here is where we can customize the properties of the tile cache that will be generated.
- In the Tiling Scheme section, choose ArcGIS Online / Bing Maps / Google Maps from the list. This specifies the scales at which maps will be tiled and cached, and this will align with the scale-dependent symbology we set in the map in ArcGIS Pro. You'll see a slider to change the range of scales at which tiles will be generated. Adjust the slider so the selected scales range from 1,115,581 - 4,514. This way, a collection of map tile images will be generated for each of the scales that are designed in our map. You could expand the range to include additional scale levels, but it wouldn't benefit our map, since a larger scale (more zoomed in) would be utilizing the symbology designed for 1:4,514. Realize, that for each larger (zoomed in) scale you add, the amount of tiles will increase by around 4, since each tile is divided in to four sub tiles at the next scale. These tiles are very small images, however, the storage requirements of all those little images really adds up as we increase scale levels, so be careful how many levels you add. I recommend not going any larger that the scale of 1:4,514.
- Leave the Image Format option set to MIXED. This specifies that the smallest possible image format will be used for each tile. This is particularly useful for the edges of your map that may be blank or other areas that are mostly transparent. JPEG files are generally the smallest storage size, but they don't support transparency like PNG files do. So areas that require transparency will be stored as PNG files and other areas will be JPEGs to minimize the amount of storage required.
- In the Options section, select the Cache Automaticaly on the Server option. This causes the server to generate all tile images at all scales immediately upon publishing the service. The other options Allow tiles to be generated on-the-fly as clients hit the service and zoom and pan across the map. Initil hits by those clients will be slightly slower, since tiles need to be created in real-time, but any subsequent requests for the same map areas and scales will utilize those tile images and be really fast.
- In the Estimate section, you can ask ArcGIS Pro to make estimates for the number to tiles and the corresponding storage space required for the cache you are planning to create. You can go back and change the number of scales in the slider and re-calculate the storage estimate to see the impact of each larger scale. The map we are caching covers a relatively small area so our storage requirements are low, but you can imagine how large these numbers can get when caching imagery at more scales and for larger areas.
- Go back to the General tab and go ahead and click Publish.
- The process of generating all the tile images takes some time. You should see a progress bar along the bottom of the ArcGIS Pro window. It should get to a message indicating the the service has been published and that caching is in progress. In a web browser, go to your Server Manager site and click on the Services Tab. Along the left, click the Hosted link and you should see your Little Rock service in the list. Next to the service's name you will see a small icon (looks like four little tiles) to View Cache Status. Click that icon and you'll see a progress window that indicates how many tiles have been generated. You may also want to open the Task Manager on your EC2 machine to see how hard it is working. Right-click the task bar at the bottom of your computer's desktop (be sure you click on your Remote Desktop EC2 computer, not your local desktop computer's task bar). Clicking the Performance tab will show how much CPU and RAM are being utilized.
- The cache you're building for this lesson should take under an hour to generate. Do not stop your instance while tile generation is in progress.
I have sometimes run into repeated crashes of the tiling processes when trying to build tiles of this map. If the reported number of tiles is not increasing when you view the status, or you get an error message about a crash, just take note of the scale level at which the tiles stopped generating, and move ahead to the next steps. It's not critical that you finish creating all the tiles for this Little Rock map; it's just for practice.
- While your tiles are being built (or afterward), take a moment to open Windows Explorer and navigate to the path: C:\arcgisserver\directories\arcgiscache\Hosted_LittleRock\Little Rock, AR\_alllayers.
Take a look around. You'll see folders for each scale level of your cache. You should also see large files with the extension .bundle. A bundle file is Esri's way of storing a large number of tile image files in one compressed file. You can optionally store each tile as an individual image file (.jpg or .png) using what ArcGIS Server calls the Exploded storage format, but when your cache starts containing thousands or millions of images it can be tedious for Windows to copy it around, assign permissions, or frankly do anything with it. Bundles are the way to go.
- When you are done creating tiles (or if you stopped because of a crash), open a web browser on your local computer and open the Services Directory. The URL will look like this: https://namegeog865####.e-education.psu.edu/server/rest/services/
- If you don't see your LittleRock service in the Hosted folder, return to the ArcGIS Server Manager (https://namegeog865####.e-education.psu.edu/server/manager) in your browser, and repeat the steps we performed in earlier lessons to make your service viewable by the public (Everyone).
- Back on the rest services page, click your LittleRock service, and choose to View in ArcGIS JavaScript.
- Zoom and pan around the map for a while, and note how quickly the tiles appear. Note that if your tile caching processes crashed, then you'll only be able to zoom in to the scale level at which the tiling stopped.
- When you are done creating and experimenting with tiles, stop your AWS Instance.
- Following the same pattern you used earlier in this lesson, open the AWS Management Console, and set your instance back to the m4.2xlarge Instance Type.