Quick Answer:

XYZ coordinates are a three-axis system that defines position in space. X is the horizontal axis (longitude or Easting), Y is the vertical axis (latitude or Northing), and Z is the third axis representing elevation, height, or depth. In satellite imagery and GIS, X and Y define where a pixel sits on the ground in 2D, and Z adds the elevation dimension for 3D terrain models, Digital Elevation Models, and 3D city models. In web mapping, Z is also used as the zoom level in map tile systems.

Intro

XYZ coordinates are the simplest way to describe where something is in space. X tells you how far left or right. Y tells you how far forward or back. Z tells you how far up or down. Together, three numbers place any point in 3D space with complete precision. In satellite imagery and GIS, XYZ is the foundation of everything from a flat map tile to a full 3D terrain model of a mountain range.

What Are XYZ Coordinates?

XYZ coordinates come from the Cartesian coordinate system. The system uses three perpendicular axes that all meet at a single point called the origin (0, 0, 0).

• X axis: Runs horizontally left and right. Positive X goes right. Negative X goes left.
• Y axis: Runs north and south in geographic systems. Positive Y goes north. Negative Y goes south.
• Z axis: Runs perpendicular to both X and Y. In physical space it represents height or depth. In geographic systems it represents elevation above or below sea level.

A Simple Real-World Example

Imagine a flagpole in an open field. You are standing at the entrance gate.

• The flagpole is 50 metres east of the gate: X = 50
• The flagpole is 30 metres north of the gate: Y = 30
• The flag at the top is 12 metres above the ground: Z = 12

The flag’s full position is (X: 50, Y: 30, Z: 12). Without the Z coordinate, you know where the pole is but not where the flag is. With Z, the position is fully defined in 3D space.

This is exactly how satellite imagery and GIS systems locate features on and above the Earth’s surface.

X and Y in Geographic and Projected Coordinate Systems

In geospatial work, X and Y coordinates take two forms depending on the coordinate reference system in use.

Geographic Coordinates (Latitude and Longitude)

In a geographic coordinate system like WGS84:

• X = Longitude: The angle east or west of the Prime Meridian in degrees. Ranges from -180 degrees to +180 degrees.
• Y = Latitude: The angle north or south of the equator in degrees. Ranges from -90 degrees to +90 degrees.

Longitude and latitude are angular measurements. One degree of longitude equals about 111km at the equator but only 55km at 60 degrees north. This makes distance and area calculations complex without spherical trigonometry.

Projected Coordinates (UTM and Others)

In a projected coordinate system like UTM WGS84:

• X = Easting: Distance in metres east of the zone’s central meridian, with a false easting of 500,000m to keep all values positive.
• Y = Northing: Distance in metres north of the equator in the northern hemisphere.

Projected coordinates are linear. One metre in X equals one metre in Y everywhere within the zone. Distance, area, and direction calculations are straightforward.

Coordinate X Y Z in Practice

The Z value is the same regardless of whether you use geographic or projected X and Y. It is always measured in metres above a defined vertical datum, most commonly Mean Sea Level or the WGS84 ellipsoid.

What Is the Z Coordinate?

Z is the dimension most people understand least because everyday navigation is mostly 2D. Maps, floor plans, and road networks work in X and Y. Elevation only matters when you need to know how high or how deep something is.

In satellite imagery and geospatial analysis, Z matters in four important ways.

Z as Elevation in Terrain Modelling

When a DEM is created from stereo satellite imagery, every pixel in the raster has an X position, a Y position, and a Z value representing the elevation of the ground at that point. A DEM of a mountain range stores X and Y to define where each measurement was taken, and Z to record the height at each point from valley floors to peaks.

From this XYZ surface data you can calculate slope, aspect, watershed boundaries, flood inundation extent, line of sight, and cut and fill volumes for construction.

Z as Building Height in 3D City Models

In a 3D city model built from tri-stereo VHR satellite data, every building has a base defined by X and Y and a height defined by Z. The Z difference between the roof surface and the street level is the building height. These XYZ models are used for urban planning, solar potential mapping, shadow analysis, and telecommunication signal propagation.

Z as Depth in Subsurface Mapping

In geological surveys, pipeline routing, and subsurface utility mapping, Z is used as depth below the surface rather than height above it. Negative Z values represent features below ground level.

Z as Deformation in InSAR Monitoring

XRTech’s SAR satellites detect changes in the Z value of a surface over time using InSAR (Interferometric SAR). By comparing two radar images of the same area taken on different dates, InSAR measures how much the ground surface has moved in the Z direction between captures. Deformation as small as 1mm to 2mm is detectable.

This is used to monitor dam wall subsidence, bridge foundation settlement, pipeline corridor ground movement, and urban subsidence in areas of groundwater extraction.

XYZ Coordinates in Web Mapping Tile Systems

Web mapping platforms including Google Maps, Mapbox, OpenStreetMap, and Leaflet use an XYZ tile system where Z means something entirely different from elevation:

• Z = Zoom level: A number from 0 (entire Earth in one tile) to 22 (individual buildings visible). Each zoom level quadruples the number of tiles.
• X = Tile column: Horizontal position in the tile grid at zoom level Z.
• Y = Tile row: Vertical position in the tile grid at zoom level Z.

At zoom level 0, one tile covers the entire Earth. At zoom level 18, one tile covers roughly 150m x 150m on the ground. Most web map tile URLs follow the pattern:

https://tiles.example.com/{Z}/{X}/{Y}.png

This tile Z is a completely separate concept from elevation Z used in GIS and 3D modelling. Both use the same letter in different contexts. When you see XYZ tiles, Z is always zoom. When you see XYZ coordinates in GIS data, Z is always elevation or height.

Position XYZ in GPS and Satellite Positioning

GPS satellites calculate your position in 3D XYZ space before converting it to the latitude, longitude, and altitude your device displays. The GPS system uses Earth-Centred Earth-Fixed (ECEF) XYZ coordinates, with the origin at the Earth’s centre of mass.

Your receiver measures the distance to at least four satellites and uses trilateration to calculate your ECEF X, Y, and Z values. It then converts those three numbers to latitude, longitude, and altitude using the WGS84 ellipsoid model.

This matters for satellite imagery because orthorectification uses GPS-derived ground control points (GCPs) with known X, Y, and Z values to anchor images to real ground coordinates. The Z value of each GCP is critical: without accurate elevation at the control points, the geometric correction of the image is incomplete and horizontal accuracy degrades.

XYZ Coordinates in XRTech Satellite Products

XRTech delivers geospatial data with full XYZ coordinate support across all 2D and 3D product types.