diff --git a/docs/legal/asset-policy.md b/docs/legal/asset-policy.md
index baa71b8..3e6f34f 100644
--- a/docs/legal/asset-policy.md
+++ b/docs/legal/asset-policy.md
@@ -18,6 +18,22 @@ The repository `.gitignore` excludes `reference/`, `.work/`, archives, disk imag
 - Synthetic test fixtures generated specifically for this project.
 - Public-domain terrain data, such as USGS/NASA datasets, when redistributed according to source terms.
 
+## Test fixture layout
+
+Project-owned synthetic terrain fixtures live under `tests/fixtures/open/`. The
+`open/` segment marks the directory as cleared for commit: every file there
+must be authored specifically for OpenVistaPro, or carry an explicit open
+license with attribution alongside it.
+
+Never place proprietary VistaPro data, extracted program files, manuals,
+screenshots, archives, disk images, or local-only reference payloads under
+`tests/`. Those belong in the git-ignored `reference/` and `.work/` directories
+and must stay local-only.
+
+Importers parse only open or synthetic formats. The `ovp-text` plain-text
+heightfield format read by `src/import.rs` is an original OpenVistaPro format;
+it is not a reimplementation of any proprietary VistaPro file layout.
+
 ## Reverse engineering boundary
 
 Use the reference copies for product behavior research only. Avoid decompilation or binary translation unless a future legal review explicitly approves a narrow compatibility investigation.
diff --git a/src/import.rs b/src/import.rs
new file mode 100644
index 0000000..7ee1d74
--- /dev/null
+++ b/src/import.rs
@@ -0,0 +1,489 @@
+//! Terrain import boundary.
+//!
+//! This module isolates open-format terrain importers from the renderer's
+//! internal model. An importer parses an external representation entirely in
+//! memory and yields an [`ImportedTerrain`]: a validated [`HeightGrid`] plus
+//! [`TerrainSourceMetadata`] recording where the data came from. Renderer and
+//! scene code only ever see the clean internal `HeightGrid`, never a
+//! source-specific format.
+//!
+//! Per `docs/legal/asset-policy.md`, importers operate only on open or
+//! synthetic data. No proprietary VistaPro file compatibility is implemented
+//! here; historical-format support is deferred to a separately reviewed
+//! clean-room plan.
+//!
+//! # The `ovp-text` format
+//!
+//! [`import_ovp_text`] reads a tiny, project-owned plain-text heightfield
+//! format authored for OpenVistaPro. It is intentionally minimal: it exists to
+//! exercise the import boundary and to give tests a human-readable fixture.
+//!
+//! ```text
+//! # comment lines start with '#'
+//! width: 3
+//! height: 2
+//! unit: meters
+//! 10 20 30
+//! 40 50 60
+//! ```
+//!
+//! Three headers are required (`width`, `height`, `unit`) and must precede the
+//! elevation rows. `unit` is `meters` or `feet`. After the headers, the body
+//! holds exactly `width * height` whitespace-separated decimal samples in
+//! row-major order. Blank lines and `#` comments are ignored anywhere.
+
+use std::fmt;
+
+use crate::terrain::{HeightGrid, TerrainError};
+
+/// Vertical unit of the elevation samples in an imported terrain source.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ElevationUnit {
+    /// Elevations expressed in metres.
+    Meters,
+    /// Elevations expressed in feet.
+    Feet,
+}
+
+impl ElevationUnit {
+    /// Lower-case identifier used in `ovp-text` headers and in `info` output.
+    pub fn as_str(self) -> &'static str {
+        match self {
+            ElevationUnit::Meters => "meters",
+            ElevationUnit::Feet => "feet",
+        }
+    }
+}
+
+impl fmt::Display for ElevationUnit {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(self.as_str())
+    }
+}
+
+/// Provenance for an imported terrain: which open format it came from, the
+/// source grid dimensions, and the vertical unit of its samples.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct TerrainSourceMetadata {
+    format: String,
+    width: u32,
+    height: u32,
+    elevation_unit: ElevationUnit,
+}
+
+impl TerrainSourceMetadata {
+    /// Build metadata for a terrain parsed from `format` with the given source
+    /// dimensions and elevation unit.
+    pub fn new(
+        format: impl Into<String>,
+        width: u32,
+        height: u32,
+        elevation_unit: ElevationUnit,
+    ) -> Self {
+        TerrainSourceMetadata {
+            format: format.into(),
+            width,
+            height,
+            elevation_unit,
+        }
+    }
+
+    /// Short identifier of the source format, e.g. `"ovp-text"`.
+    pub fn format(&self) -> &str {
+        &self.format
+    }
+
+    /// Width of the source grid in samples.
+    pub fn width(&self) -> u32 {
+        self.width
+    }
+
+    /// Height of the source grid in samples.
+    pub fn height(&self) -> u32 {
+        self.height
+    }
+
+    /// Vertical unit the source expressed elevations in.
+    pub fn elevation_unit(&self) -> ElevationUnit {
+        self.elevation_unit
+    }
+}
+
+/// A terrain parsed from an open external format: the validated internal
+/// [`HeightGrid`] paired with [`TerrainSourceMetadata`] describing its origin.
+#[derive(Debug, Clone)]
+pub struct ImportedTerrain {
+    grid: HeightGrid,
+    metadata: TerrainSourceMetadata,
+}
+
+impl ImportedTerrain {
+    /// Pair a parsed `grid` with its source `metadata`.
+    pub fn new(grid: HeightGrid, metadata: TerrainSourceMetadata) -> Self {
+        ImportedTerrain { grid, metadata }
+    }
+
+    /// Borrow the internal height grid.
+    pub fn grid(&self) -> &HeightGrid {
+        &self.grid
+    }
+
+    /// Borrow the source metadata.
+    pub fn metadata(&self) -> &TerrainSourceMetadata {
+        &self.metadata
+    }
+
+    /// Consume the imported terrain, returning just the internal height grid.
+    pub fn into_grid(self) -> HeightGrid {
+        self.grid
+    }
+}
+
+/// Errors produced while importing terrain from an open external format.
+#[derive(Debug)]
+pub enum ImportError {
+    /// The source declared a zero width or height.
+    InvalidDimensions {
+        /// Declared source width.
+        width: u32,
+        /// Declared source height.
+        height: u32,
+    },
+    /// The source payload was structurally malformed: a missing or unknown
+    /// header, an unparseable number, or otherwise unreadable content.
+    MalformedSource(String),
+    /// The number of elevation samples did not match the declared dimensions.
+    SampleCountMismatch {
+        /// Sample count implied by the declared dimensions.
+        expected: usize,
+        /// Sample count actually found in the source body.
+        actual: usize,
+    },
+    /// Constructing the internal [`HeightGrid`] from parsed data failed.
+    Grid(TerrainError),
+}
+
+impl fmt::Display for ImportError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ImportError::InvalidDimensions { width, height } => write!(
+                f,
+                "imported terrain has invalid dimensions {width}x{height}; \
+                 width and height must be non-zero"
+            ),
+            ImportError::MalformedSource(detail) => {
+                write!(f, "malformed terrain source: {detail}")
+            }
+            ImportError::SampleCountMismatch { expected, actual } => write!(
+                f,
+                "expected {expected} elevation samples for the declared dimensions, got {actual}"
+            ),
+            ImportError::Grid(e) => write!(f, "could not build height grid from import: {e}"),
+        }
+    }
+}
+
+impl std::error::Error for ImportError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            ImportError::Grid(e) => Some(e),
+            _ => None,
+        }
+    }
+}
+
+impl From<TerrainError> for ImportError {
+    fn from(e: TerrainError) -> Self {
+        ImportError::Grid(e)
+    }
+}
+
+/// Format identifier recorded for terrains parsed by [`import_ovp_text`].
+pub const OVP_TEXT_FORMAT: &str = "ovp-text";
+
+/// Import a terrain from the project-owned `ovp-text` plain-text heightfield
+/// format described in the module documentation.
+///
+/// The entire source is parsed in memory; no filesystem or network access is
+/// performed. Callers that have a file path read it themselves and pass the
+/// contents here, which keeps the importer easy to test and reuse.
+pub fn import_ovp_text(source: &str) -> Result<ImportedTerrain, ImportError> {
+    let mut width: Option<u32> = None;
+    let mut height: Option<u32> = None;
+    let mut unit: Option<ElevationUnit> = None;
+    let mut samples: Vec<f32> = Vec::new();
+    let mut seen_sample = false;
+
+    for raw in source.lines() {
+        let line = raw.trim();
+        if line.is_empty() || line.starts_with('#') {
+            continue;
+        }
+
+        if let Some((key, value)) = line.split_once(':') {
+            if seen_sample {
+                return Err(ImportError::MalformedSource(format!(
+                    "header field {:?} appears after elevation samples",
+                    key.trim()
+                )));
+            }
+            let key = key.trim();
+            let value = value.trim();
+            match key {
+                "width" => width = Some(parse_dimension(key, value)?),
+                "height" => height = Some(parse_dimension(key, value)?),
+                "unit" => unit = Some(parse_unit(value)?),
+                other => {
+                    return Err(ImportError::MalformedSource(format!(
+                        "unknown header field {other:?}"
+                    )));
+                }
+            }
+        } else {
+            seen_sample = true;
+            for token in line.split_whitespace() {
+                let value: f32 = token.parse().map_err(|_| {
+                    ImportError::MalformedSource(format!("invalid elevation sample {token:?}"))
+                })?;
+                samples.push(value);
+            }
+        }
+    }
+
+    let width =
+        width.ok_or_else(|| ImportError::MalformedSource("missing 'width' header".to_string()))?;
+    let height = height
+        .ok_or_else(|| ImportError::MalformedSource("missing 'height' header".to_string()))?;
+    let unit =
+        unit.ok_or_else(|| ImportError::MalformedSource("missing 'unit' header".to_string()))?;
+
+    if width == 0 || height == 0 {
+        return Err(ImportError::InvalidDimensions { width, height });
+    }
+
+    let expected = (width as usize) * (height as usize);
+    if samples.len() != expected {
+        return Err(ImportError::SampleCountMismatch {
+            expected,
+            actual: samples.len(),
+        });
+    }
+
+    let grid = HeightGrid::new(width, height, samples)?;
+    let metadata = TerrainSourceMetadata::new(OVP_TEXT_FORMAT, width, height, unit);
+    Ok(ImportedTerrain::new(grid, metadata))
+}
+
+fn parse_dimension(key: &str, value: &str) -> Result<u32, ImportError> {
+    value
+        .parse()
+        .map_err(|_| ImportError::MalformedSource(format!("invalid {key} value {value:?}")))
+}
+
+fn parse_unit(value: &str) -> Result<ElevationUnit, ImportError> {
+    match value {
+        "meters" => Ok(ElevationUnit::Meters),
+        "feet" => Ok(ElevationUnit::Feet),
+        other => Err(ImportError::MalformedSource(format!(
+            "unknown elevation unit {other:?} (expected \"meters\" or \"feet\")"
+        ))),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::terrain::HeightGrid;
+
+    // ---- TerrainSourceMetadata ----
+
+    #[test]
+    fn metadata_records_format_dimensions_and_units() {
+        let meta = TerrainSourceMetadata::new("hgt", 1201, 1201, ElevationUnit::Meters);
+        assert_eq!(meta.format(), "hgt");
+        assert_eq!(meta.width(), 1201);
+        assert_eq!(meta.height(), 1201);
+        assert_eq!(meta.elevation_unit(), ElevationUnit::Meters);
+    }
+
+    #[test]
+    fn elevation_unit_displays_human_readable_name() {
+        assert_eq!(ElevationUnit::Meters.to_string(), "meters");
+        assert_eq!(ElevationUnit::Feet.to_string(), "feet");
+    }
+
+    // ---- ImportedTerrain ----
+
+    #[test]
+    fn imported_terrain_exposes_grid_and_metadata() {
+        let grid = HeightGrid::plane(2, 2).unwrap();
+        let meta = TerrainSourceMetadata::new("ovp-text", 2, 2, ElevationUnit::Meters);
+        let imported = ImportedTerrain::new(grid, meta.clone());
+        assert_eq!(imported.grid().width(), 2);
+        assert_eq!(imported.grid().height(), 2);
+        assert_eq!(imported.metadata(), &meta);
+    }
+
+    #[test]
+    fn imported_terrain_into_grid_yields_owned_height_grid() {
+        let grid = HeightGrid::plane(3, 1).unwrap();
+        let meta = TerrainSourceMetadata::new("ovp-text", 3, 1, ElevationUnit::Meters);
+        let imported = ImportedTerrain::new(grid, meta);
+        let owned: HeightGrid = imported.into_grid();
+        assert_eq!(owned.width(), 3);
+        assert_eq!(owned.height(), 1);
+    }
+
+    // ---- ImportError ----
+
+    #[test]
+    fn invalid_dimensions_error_is_displayable() {
+        let err = ImportError::InvalidDimensions {
+            width: 0,
+            height: 4,
+        };
+        let msg = err.to_string();
+        assert!(msg.contains("dimension"), "got: {msg:?}");
+        assert!(msg.contains('0') && msg.contains('4'), "got: {msg:?}");
+    }
+
+    #[test]
+    fn malformed_source_error_is_displayable() {
+        let err = ImportError::MalformedSource("missing 'width' header".to_string());
+        assert!(err.to_string().contains("missing 'width' header"));
+    }
+
+    #[test]
+    fn sample_count_mismatch_error_is_displayable() {
+        let err = ImportError::SampleCountMismatch {
+            expected: 6,
+            actual: 5,
+        };
+        let msg = err.to_string();
+        assert!(msg.contains('6') && msg.contains('5'), "got: {msg:?}");
+    }
+
+    #[test]
+    fn import_error_is_std_error() {
+        fn assert_error<E: std::error::Error>(_: &E) {}
+        assert_error(&ImportError::MalformedSource("x".into()));
+    }
+
+    // ---- import_ovp_text ----
+
+    #[test]
+    fn imports_tiny_ovp_text_heightfield() {
+        let source = "\
+width: 3
+height: 2
+unit: meters
+10 20 30
+40 50 60
+";
+        let imported = import_ovp_text(source).expect("valid ovp-text should import");
+        assert_eq!(imported.grid().width(), 3);
+        assert_eq!(imported.grid().height(), 2);
+        assert_eq!(imported.grid().sample(0, 0), Some(10.0));
+        assert_eq!(imported.grid().sample(2, 1), Some(60.0));
+        assert_eq!(imported.metadata().format(), "ovp-text");
+        assert_eq!(imported.metadata().width(), 3);
+        assert_eq!(imported.metadata().height(), 2);
+        assert_eq!(imported.metadata().elevation_unit(), ElevationUnit::Meters);
+    }
+
+    #[test]
+    fn import_skips_comments_and_blank_lines() {
+        let source = "\
+# OpenVistaPro plain-text heightfield
+
+width: 2
+height: 2
+unit: feet
+
+# elevation rows follow
+1 2
+3 4
+";
+        let imported = import_ovp_text(source).expect("comments and blanks should be ignored");
+        assert_eq!(imported.metadata().elevation_unit(), ElevationUnit::Feet);
+        assert_eq!(imported.grid().sample(1, 1), Some(4.0));
+    }
+
+    #[test]
+    fn import_rejects_missing_header_field() {
+        let source = "width: 2\nheight: 2\n1 2\n3 4\n";
+        let err = import_ovp_text(source).expect_err("missing unit header must be rejected");
+        assert!(
+            matches!(err, ImportError::MalformedSource(_)),
+            "got: {err:?}"
+        );
+    }
+
+    #[test]
+    fn import_rejects_zero_dimensions() {
+        let source = "width: 0\nheight: 2\nunit: meters\n";
+        let err = import_ovp_text(source).expect_err("zero width must be rejected");
+        assert!(
+            matches!(
+                err,
+                ImportError::InvalidDimensions {
+                    width: 0,
+                    height: 2
+                }
+            ),
+            "got: {err:?}"
+        );
+    }
+
+    #[test]
+    fn import_rejects_unparseable_sample() {
+        let source = "width: 2\nheight: 1\nunit: meters\n1 oops\n";
+        let err = import_ovp_text(source).expect_err("non-numeric sample must be rejected");
+        assert!(
+            matches!(err, ImportError::MalformedSource(_)),
+            "got: {err:?}"
+        );
+    }
+
+    #[test]
+    fn import_rejects_sample_count_mismatch() {
+        let source = "width: 3\nheight: 2\nunit: meters\n1 2 3\n4 5\n";
+        let err = import_ovp_text(source).expect_err("short sample grid must be rejected");
+        assert!(
+            matches!(
+                err,
+                ImportError::SampleCountMismatch {
+                    expected: 6,
+                    actual: 5
+                }
+            ),
+            "got: {err:?}"
+        );
+    }
+
+    #[test]
+    fn import_rejects_unknown_unit() {
+        let source = "width: 1\nheight: 1\nunit: cubits\n7\n";
+        let err = import_ovp_text(source).expect_err("unknown unit must be rejected");
+        assert!(
+            matches!(err, ImportError::MalformedSource(_)),
+            "got: {err:?}"
+        );
+    }
+
+    #[test]
+    fn imports_project_owned_fixture_from_disk() {
+        let path = concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/tests/fixtures/open/tiny-heightfield.ovptext"
+        );
+        let text = std::fs::read_to_string(path).expect("fixture file should be readable");
+        let imported = import_ovp_text(&text).expect("fixture should import cleanly");
+        assert_eq!(imported.grid().width(), 3);
+        assert_eq!(imported.grid().height(), 2);
+        assert_eq!(imported.grid().sample(0, 0), Some(1.0));
+        assert_eq!(imported.grid().sample(2, 1), Some(6.0));
+        assert_eq!(imported.metadata().format(), "ovp-text");
+        assert_eq!(imported.metadata().elevation_unit(), ElevationUnit::Meters);
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 3a1b346..50590fd 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,5 +1,6 @@
 pub mod cli;
 pub mod colormap;
+pub mod import;
 pub mod render;
 pub mod scene;
 pub mod scene_file;
diff --git a/tests/fixtures/open/tiny-heightfield.ovptext b/tests/fixtures/open/tiny-heightfield.ovptext
new file mode 100644
index 0000000..907c230
--- /dev/null
+++ b/tests/fixtures/open/tiny-heightfield.ovptext
@@ -0,0 +1,8 @@
+# OpenVistaPro plain-text heightfield fixture (ovp-text format)
+# Project-owned synthetic data authored for OpenVistaPro tests.
+# See docs/legal/asset-policy.md for the fixture/data policy.
+width: 3
+height: 2
+unit: meters
+1 2 3
+4 5 6