# Mathematical rule to convert between degrees and centimeters based upon projection

I have some Tanzania drone imagery data in a local geographic projection EPSG:32737 that uses the unit of meters. Then I have other vector data that is in EPSG:4326 which is denominated in degrees. In order to map the vector data on the imagery, I converted the imagery over to 4326. Since I believe 4326 is the most popular projection, I figured having all data in that projection would make things easier and avoid inadvertent projection errors.

The problem is that I want to resample the imagery to a lower resolution. In the original projection the units were meters but in 4326 the units are degrees. So my question is, is there a simple rule of thumb to convert between degrees and meters--given some local projection? Like what is the algorithm to compute this. Note the total study area is about 2 miles x 2 miles in size, since the resolution is so high.

Note, I understand that a degree corresponds to a different number of meters, depending on where on earth the imagery or geography is captured. So that is fine. But given that I am using EPSG:32737 versus EPSG:4326, I want to know

A more precise definition of the problem is this. The original imagery is 6cm resolution, and that is in EPSG:32737. After converting the image to EPSG:4326, I want to resample the image to 1 meter resolution. So how many degrees correspond to 1 meter distance in Tanzania? Is there a simple equation to do this, or is there some package or website I can use?

In terms of tools, I was using `rasterio` and `GDAL` in python. I would like to do this through code instead of through a tool like `QGIS`.

• How large is your study area? – Kirk Kuykendall Sep 18 at 22:17
• The study area is not very large, since the resolution is so high. So the area is on the order of 2miles x 2 miles square. – krishnab Sep 18 at 22:29
• Can you resample the 6cm to 1m in 32737(meters), then project that to 4326, just a different order. – klewis Sep 18 at 22:40
• I would work in EPSG:32737 (WGS84 UTM Zone 37 North) if your study area is less than 3 DD wide from the central meridian (39 degrees), it's usually much quicker to project vector than to project a raster; both are based on the WGS84 datum so no special transformation is required. An added bonus is that shape_length and shape_area actually have meaning. – Michael Stimson Sep 19 at 5:33
• If you create lines at exact distances, 1 meter, for example in 32737 and project the lines to 4326, you will find the equivalent distance in decimal degree. – klewis Sep 19 at 16:56