Coordinate Systems and Projections for GIS: EPSG, WGS84, MSK

Coordinate systems are the first thing that confuses GIS beginners. Why don't coordinates in QGIS match those in AutoCAD? Why is the polygon area calculated incorrectly? Why has the map "shifted" by 200 meters? Usually the cause is the wrong projection.

Geographic vs Projected Coordinates

There are two fundamentally different ways to specify a position on Earth:

Geographic coordinates — latitude and longitude in degrees. Earth is treated as an ellipsoid. Example: Moscow — 55.7558 N, 37.6176 E. You cannot directly measure distances in degrees — 1 degree of latitude (111 km) is not equal to 1 degree of longitude (depends on latitude: from 111 km at the equator to 0 km at the pole).

Projected coordinates — X and Y in meters on a plane. Earth is "unfolded" onto a flat surface through a mathematical projection. Example: UTM zone 37N — X=37,500,000, Y=6,200,000. Distances and areas can be calculated directly.

Key Coordinate Systems

WGS 84 (EPSG:4326)

Global geographic system. Coordinates in degrees (latitude, longitude). Used by GPS, OpenStreetMap, GeoJSON (by specification). This is the "default" coordinate system for most geodata.

Web Mercator (EPSG:3857)

Projection for web maps. Used by Google Maps, Yandex Maps, OpenStreetMap tiles, Leaflet, Mapbox. Coordinates in meters, but distorts areas (Greenland appears as large as Africa). Not suitable for accurate measurements.

UTM (Universal Transverse Mercator)

The world is divided into 60 zones of 6 degrees longitude each. Each zone has its own projection with minimal distortions. Moscow is in zone 37N (EPSG:32637). St. Petersburg is in zone 36N (EPSG:32636).

Zone = floor((longitude + 180) / 6) + 1
EPSG = 32600 + zone  (northern hemisphere)
EPSG = 32700 + zone  (southern hemisphere)

MSK (Russian Local Coordinate Systems)

In Russia, local coordinate systems (MSK) are used for cadastre and land surveying. Each federal subject has 1-3 zones with unique parameters. On osm2cdr.ru the export list offers 122 Gauss-Kruger zones keyed to MSK numbers, covering 85 numbers: an approximation, not the true MSK of a subject; the parameters of 229 real zones across 75 MSK numbers, each with a named source and confidence class, are computed by the coordinate converter.

Examples: - MSK-77 (Moscow) — unofficial EPSG, zones 1-2. - MSK-78 (St. Petersburg) — zone 1. - MSK-50 (Moscow Oblast) — zones 1-3.

Important: MSK coordinates are not compatible between regions. You cannot "merge" MSK-77 and MSK-50 data without transformation.

How to Choose a Projection

Coordinate Transformation

GDAL/OGR

# Reproject Shapefile from WGS84 to UTM 37N
ogr2ogr -t_srs EPSG:32637 output_utm.shp input_wgs84.shp

# GeoJSON to MSK-77 zone 1
ogr2ogr -t_srs "+proj=tmerc +lat_0=55.66666 +lon_0=37.5 +k=1 +x_0=1300000 +y_0=0 +ellps=bessel +units=m" \
  output_msk77.geojson input.geojson

Python (pyproj)

from pyproj import Transformer

transformer = Transformer.from_crs("EPSG:4326", "EPSG:32637", always_xy=True)
x, y = transformer.transform(37.6176, 55.7558)
print(f"UTM 37N: X={x:.2f}, Y={y:.2f}")
# UTM 37N: X=413932.84, Y=6179346.17

PostGIS

SELECT ST_Transform(
  ST_SetSRID(ST_MakePoint(37.6176, 55.7558), 4326),
  32637
) AS point_utm;

Export with the Correct Projection

On osm2cdr.ru, when exporting a map you can choose a coordinate system from 165 available: 43 popular ones (WGS84, Web Mercator, UTM zones, national systems) and 122 Gauss-Kruger zones keyed to MSK numbers for Russia — an approximation, not the true MSK of a subject; the parameters of 229 real zones across 75 MSK numbers, each with a named source and confidence class, are computed by the coordinate converter.

Select the area, format (DWG, DXF, Shapefile, GeoJSON, etc.), and CRS. The service will perform the transformation automatically via PostGIS and GDAL.

The right projection is the foundation of accurate maps. Export data in the correct CRS at osm2cdr.ru.