For most surveys, you do not need to worry about Offline Maps. When on-site, if you have a good/fair connection to the internet then the OTISS survey apps will be able to display the required maps and use them for your surveying. The survey apps will automatically store parts of the maps on the phone/tablet’s SD card to increase performance and reduce 4G/3G data usage – but you don’t have to do anything.
However, for areas of poor 4G/3G mobile signal, you will want to pre-load the maps before you leave your home/office. So you need to read this page and use the Download Maps feature on the OTISS survey apps.
NB: Not all maps can be stored offline in this way. All the maps, drawings and plans that you have loaded into OTISS, and also OpenStreetMap can be stored. But for licensing reasons – the Google maps cannot be stored offline (yet).
What are Offline Maps?
OTISS provides you access to the worldwide OpenStreetMap and Google road/aerial maps. And, on the OTISS website, you can also upload your own maps, drawings and plans and assign them to the survey sites. The mobile survey app lets you view and zoom around these maps – downloading the appropriate map tiles from the internet as they are needed, i.e. from the ‘online’ OpenStreetMap and OTISS servers.
The survey apps can also download the relevant parts of these maps to the phone/tablet’s SD card. These map tiles/images are now stored ‘offline’. These ‘offline’ maps are then used rather than reloading the ‘online’ images from the internet.
What are map tiles?
Map tiles are square bitmap graphics that are displayed in a grid arrangement to show a map. OTISS, and the other internet map providers, break up large maps into a grid of standard sized map tiles. This app works in the same way as your internet browser – it only downloads those tiles that are needed to display the visible area at the current zoom level. Panning or zooming the map will require a new set of tiles to be downloaded.
Auto Offline Maps
When the Auto Offline Maps feature is enabled, as you pan and zoom around a map, the map tiles are automatically stored ‘offline’ on your device’s SD card. This is the normal mode of operation – you don’t need to do anything. Press the Settings Icon to turn the Auto Offline Maps on and off.
Download Offline Maps
For survey areas with poor 4G/3G signal, you can preload the offline maps before leaving your home or office (i.e. with a Wi-Fi connection).
- Download a survey to the mobile device.
- From the list of Downloaded Surveys, you can select a survey and goto the Download Maps page.
- The Layers menu can be used to select the map layer you wish to download – typically your site map/plan or OpenStreetMap
- Pan and zoom to the appropriate section of the map.
- Everything you see on the map will be downloaded at all zoom levels.
- Press the Download button and wait for the messages to say that the download is complete.
- Larger sections take longer to download – this is because a separate set of map tiles must be downloaded for each zoom level. So it will be quicker if you select only the area you actually need. The Download button will disappear if the area is too large to download in one go – just zoom in a level or two. Large maps will need to be downloaded in several sections.
- For larger sites, the lowest zoom level(s) of the map may not be needed or may not be clear enough.
In this case, you can reduce the “Max zoom level” (e.g. from 24 to 22 or 21) to remove these lowest levels. This allows for faster downloads of the same area, or being able to download larger areas – i.e. without the lowest zoom levels.
- Repeating the Download may be useful: (a) to verify that all the map tiles have been downloaded; or (b) to retry the download if the previous attempt failed. In all cases, only new map tiles will be downloaded, the existing ones will be checked (but not downloaded again).
Note: Older Android devices (4.x) and lower specification devices may not be able to complete downloads of large areas – just do a series of smaller areas.
These offline map tiles do take up space on your SD card. It is recommended that you delete the offline map tiles for a survey when they are no longer needed. These tiles are automatically deleted when you remove the survey from the app.
Turn the automatic offline caching on and off.
Press the Delete button to Delete button to remove the offline map tiles for this survey.