Georeferenced Images

Android only

Georeferenced image overlays are currently available on Android only. iOS support is planned for a future release.

Mapit GIS Professional can display georeferenced raster images as map overlays. This is ideal for drone orthophotos, scanned paper maps, historical aerial imagery, or any raster image that has been georeferenced to real-world coordinates.

Supported formats

GeoTIFF (.tif, .tiff)

GeoTIFF is the most common georeferenced image format. It embeds coordinate system information and geographic bounds directly in the TIFF file headers - no additional files are needed.

Feature	Supported
Compression	Uncompressed, LZW, JPEG, Deflate, PackBits
Layout	Stripped and tiled TIFFs
Color	RGB, RGBA, grayscale, palette/indexed color, YCbCr
Bit depth	8-bit
Coordinate systems	Any EPSG code + user-defined Transverse Mercator (auto-reprojected to WGS84 with quadrilateral placement)
Max file size	50 MB

JPEG with world file (.jpg + .jgw)

Standard JPEG images can be georeferenced using a companion world file. The world file is a small text file that defines the image's position and scale in map coordinates.

World file extensions for JPEG: .jgw, .jpgw, .wld

PNG with world file (.png + .pgw)

PNG images work the same way as JPEG, with their own world file extension.

World file extensions for PNG: .pgw, .pngw, .wld

TIFF with world file (.tif + .tfw)

Standard TIFF files (without embedded GeoTIFF tags) can also use a companion world file. If a TIFF file has both embedded GeoTIFF tags and a world file, the embedded tags take priority.

World file extensions for TIFF: .tfw, .tifw, .wld

What is a world file?

A world file is a plain text sidecar file that describes how an image maps to real-world coordinates. It contains six lines defining an affine transformation:

0.25          Line 1: pixel size in X direction (meters/pixel)
0.0           Line 2: rotation about Y axis (usually 0)
0.0           Line 3: rotation about X axis (usually 0)
-0.25         Line 4: pixel size in Y direction (usually negative)
311334.625    Line 5: X coordinate of the center of the upper-left pixel
5523336.625   Line 6: Y coordinate of the center of the upper-left pixel

The world file must:

• Be in the same folder as the image
• Have the same base filename as the image (e.g. photo.jpg + photo.jgw)

tip

World files do not contain coordinate system (CRS) information. When you import an image with a world file, Mapit GIS will check whether the coordinates are in WGS84 (latitude/longitude). If the coordinates are in a projected system (e.g. UTM), you will be prompted to enter the EPSG code so the image can be correctly placed on the map.

Common EPSG codes:

• 4326 - WGS 84 (latitude/longitude)
• 3857 - Web Mercator
• 326xx - WGS 84 / UTM Zone xxN (e.g. 32611 for Zone 11N)
• 269xx - NAD83 / UTM Zone xxN (e.g. 26911 for Zone 11N)

If you are unsure of the EPSG code, check the source software that produced the image or look for a .prj file alongside the world file.

Importing a georeferenced image

GeoTIFF files

1. Open Offline Maps from the main menu
2. Switch to the Geo Images tab
3. Tap the + button
4. Browse to and select your .tif or .tiff file
5. The image will be imported, decoded, and placed on the map using the embedded georeferencing

JPEG, PNG, or TIFF with world file

1. Open Offline Maps from the main menu
2. Switch to the Geo Images tab
3. Tap the + button
4. Select your image file (.jpg, .jpeg, .png, .tif, or .tiff)
5. When prompted, select the companion world file (.jgw, .pgw, .tfw, etc.)
6. If the coordinates are projected, enter the EPSG code when asked
7. The image will be imported and placed on the map

Why two file selections?

Due to Android security restrictions, the file picker only grants access to the single file you select - it cannot automatically read other files in the same folder. This is why you need to select the world file separately after the image.

Managing georeferenced images

Once imported, georeferenced images appear in the Geo Images tab of the Offline Maps screen. You can:

• Toggle visibility - show or hide the image overlay
• Adjust transparency - blend the image with the base map (0-100%)
• Reorder layers - drag and drop to change stacking order
• Zoom to extent - jump to the area covered by the image
• Delete - remove the image from the list and delete the file

Creating georeferenced images

From drone software

Most drone mapping software (DJI Terra, Pix4D, DroneDeploy, OpenDroneMap) exports orthomosaic results as GeoTIFF files. These can be imported directly into Mapit GIS.

From QGIS

To export a georeferenced image from QGIS:

1. Load your raster layer in QGIS
2. Right-click the layer > Export > Save As...
3. Choose GeoTIFF as the format
4. Set the CRS and extent
5. Click OK to export

Alternatively, to create a world file:

1. Right-click the raster layer > Export > Save As...
2. Choose JPEG or PNG as the format
3. Check Create world file in the export options
4. This will produce both the image and its companion world file

Georeferencing scanned maps

To georeference a scanned paper map:

1. Open QGIS and go to Layer > Georeferencer
2. Load the scanned image
3. Add ground control points (GCPs) by clicking known locations on the image and entering their real-world coordinates
4. Run the georeferencing - QGIS will produce a GeoTIFF output

Limitations

• 50 MB file size limit - larger files are rejected at import. For larger areas, consider converting to MBTiles instead
• 8-bit color depth only - 16-bit or 32-bit GeoTIFFs are not supported
• No Cloud-Optimized GeoTIFF (COG) streaming - the entire file must be on the device
• No multi-band support - only RGB, RGBA, grayscale, and palette/indexed color images
• Full resolution rendering - the image is loaded at full resolution at all zoom levels (no pyramids). Very large images may be slow to render

Example data sources

Ordnance Survey 1:250,000 Scale Colour Raster

The OS 250k Colour Raster is a free download from the Ordnance Survey Data Hub. It provides overview mapping of Great Britain at 1:250,000 scale as GeoTIFF tiles in British National Grid (EPSG:27700).

To use in Mapit GIS:

1. Download the dataset from the OS Data Hub (free registration required)
2. Extract the ZIP - each grid square is a separate .tif file (e.g. NN.tif, SU.tif)
3. Import individual tiles via the Geo Images tab
4. Mapit GIS will automatically detect the EPSG:27700 coordinate system and reproject to WGS84

tip

Each tile covers a 100km x 100km OS grid square. For fieldwork, import only the tiles covering your area of interest rather than the entire dataset.

USGS Topographic Maps (GeoTIFF)

The USGS provides free topographic map GeoTIFFs via the topoView website. These are high-quality 1:24,000 scale maps available for the entire United States.

To use in Mapit GIS:

1. Visit topoView and navigate to your area
2. Click on a map quad and download the GeoTIFF version (not the GeoPDF)
3. Import the .tif file via the Geo Images tab
4. Mapit GIS will automatically detect the coordinate system and reproject to WGS84

note

USGS topo GeoTIFFs use a custom Transverse Mercator projection (not standard UTM). Mapit GIS handles this automatically by reading the projection parameters from the GeoTIFF metadata.