GIS Data Management Flashcards

Question 1

What is the difference between vector and raster data models?

Accepted Answer

Vector data represents geographic features as points, lines, and polygons defined by coordinates, which suits discrete objects such as roads, parcels, and wells. Raster data divides space into a regular grid of cells, each holding a value, which suits continuous phenomena such as elevation, temperature, or satellite imagery.

Question 2

What is a coordinate reference system and why does it matter?

Accepted Answer

A coordinate reference system is the framework that links numeric coordinates to real locations on Earth, defining the datum, projection, and units. It matters because the same coordinate pair can point to different places under different systems, so layers must share a common system or be transformed before they are overlaid or measured.

Question 3

What is a datum, and how does it differ from a projection?

Accepted Answer

A datum is a model of the Earth's shape and a reference point that anchors coordinates to the real surface, often defined by an ellipsoid and an origin. A projection is a mathematical method for flattening that curved surface onto a plane so that it can be drawn on a map.

Question 4

What does spatial resolution mean for a raster dataset?

Accepted Answer

Spatial resolution is the ground dimension that each raster cell represents, such as one meter or thirty meters per side. Finer resolution captures more detail but produces larger files, while coarser resolution reduces detail and storage needs. Choosing a resolution is therefore a tradeoff between accuracy and practicality for the question being asked.

Question 5

What are attributes in a GIS dataset, and how are they linked to geometry?

Accepted Answer

Attributes are descriptive values stored for each feature, such as a parcel owner, road class, or land use code, usually held in a table. Each row in the attribute table corresponds to one feature, and a shared identifier links that row to the geometry that draws it on the map.

Question 6

Why do topology rules matter for vector data?

Accepted Answer

Topology describes how features share space, such as whether lines connect at endpoints or polygons overlap or leave gaps between them. Topology rules enforce these relationships so that boundaries are consistent, for example ensuring adjacent parcels do not overlap. Clean topology prevents errors in area calculation, network analysis, and editing.

Question 7

What is the minimum mapping unit, and why is it used?

Accepted Answer

The minimum mapping unit is the smallest area or feature length that a dataset is designed to represent, with anything smaller omitted or merged into neighbors. It is used to control data volume and to match the level of detail that a map or analysis needs.

Question 8

How does scale affect the choice of data source and detail?

Accepted Answer

Scale is the ratio between a map distance and the real distance it represents. Large scale maps show small areas in fine detail, while small scale maps generalize broad regions. Source data should match the intended scale, since detailed data for a regional map adds false precision.

Question 9

What is metadata in the context of GIS data management?

Accepted Answer

Metadata is structured information that describes a dataset, including its content, origin, creator, date of creation, coverage, and the conditions for its use. Good metadata lets someone decide whether a dataset fits their purpose without opening it, and it preserves knowledge that would otherwise be lost when staff move on.

Question 10

Which elements should a basic dataset description always include?

Accepted Answer

A basic description should identify the title, the producing organization, the purpose, the spatial extent, and the coordinate reference system. It should also state the time period the data represents, the source and method of collection, the update frequency, and any known limitations or usage restrictions.

Question 11

What is lineage in metadata, and why does it matter?

Accepted Answer

Lineage is the documented history of a dataset, recording its sources, the processes applied to them, and the steps that produced the current version. It matters because users can judge reliability and reproduce results only when they know how the data was derived, including transformations, generalizations, and any errors corrected along the way.

Question 12

Why should metadata be created at the time data is produced rather than later?

Accepted Answer

Metadata is easiest and most accurate when the person who made the data records it during production, while methods, sources, and decisions are still fresh. Waiting until later often leads to missing details, guessed values, or lost context, which weakens trust and makes the dataset harder to reuse.

Question 13

What is a data dictionary, and how does it relate to metadata?

Accepted Answer

A data dictionary is a reference that defines each field in a dataset, listing its name, data type, allowed values or domain, units, and meaning. It is a component of documentation that sits alongside metadata, giving users the field level detail that dataset level metadata usually does not include.

Question 14

Why should metadata record the coordinate reference system explicitly?

Accepted Answer

Recording the coordinate reference system in metadata prevents users from guessing it, which is a common source of misaligned layers and incorrect measurements. An explicit record tells anyone reading the dataset how its coordinates relate to the Earth and whether a transformation is needed before combining it with other data.

Question 15

What does it mean for metadata to be machine readable?

Accepted Answer

Machine readable metadata is written in a consistent, structured format that software can parse, search, and validate automatically, rather than existing only as free text in a document. This allows catalogs to index datasets, tools to fill in fields, and systems to check that required elements are present.

Question 16

How does a metadata record support data reuse by people outside the original project?

Accepted Answer

A metadata record gives outside users the information they need to judge fitness for use, including what the data measures, how it was collected, and what limitations apply. It lets new analysts apply the data correctly, cite it properly, and avoid repeating problems the original producers already documented.

Question 17

What is the difference between accuracy and precision in spatial data?

Accepted Answer

Accuracy describes how close a recorded value is to the true or accepted value, while precision describes how finely the value is recorded and how consistently repeated measurements agree. A dataset can be precise yet inaccurate, such as coordinates recorded to many decimal places that are consistently offset from their true locations.

Question 18

What are the main dimensions used to assess spatial data quality?

Accepted Answer

Commonly taught quality dimensions include positional accuracy, attribute accuracy, logical consistency, completeness, and temporal accuracy. Positional accuracy concerns where features sit, attribute accuracy concerns the correctness of recorded values, consistency concerns whether rules and topology hold, completeness concerns missing features, and temporal accuracy concerns whether the data reflects the correct time.

Question 19

How can positional accuracy of a dataset be assessed?

Accepted Answer

Positional accuracy is commonly assessed by comparing dataset locations with coordinates of the same features from a source of higher accuracy, such as surveyed control points or a trusted reference layer. The differences are summarized statistically, often as a root mean square error, which describes the typical size of positional error.

Question 20

What is a topological error, and how can it be detected?

Accepted Answer

A topological error is a violation of the spatial relationships a dataset should follow, such as overlapping polygons that should not overlap, gaps between adjoining parcels, or dangling line ends in a network. These errors are found by running validation rules that flag features breaking the defined relationships, then reviewing each flagged feature.

Question 21

What is attribute accuracy, and how is it typically checked?

Accepted Answer

Attribute accuracy is the degree to which recorded descriptive values, such as road classes, owner names, or land use codes, correctly reflect the real features they describe. It is checked by comparing a sample of records against authoritative sources or field observations, then calculating the proportion of values found to be correct.

Question 22

What is data completeness, and what problems does incompleteness cause?

Accepted Answer

Data completeness is the extent to which all expected features, attributes, and coverage are present in a dataset for its intended area and time. Missing features or values can bias maps and analyses, for example when a service area study omits a neighborhood.

Question 23

What are common sources of error in GIS data collection?

Accepted Answer

Common sources include errors in original measurements, such as GPS drift or misread survey notes, errors introduced during digitizing or data entry, and generalization or processing steps that alter features. Other sources include outdated source material, incorrect coordinate transformations, and conceptual errors where a definition does not fit the question.

Question 24

Why does data lineage help when a quality problem is discovered?

Accepted Answer

Lineage records the sources and processing steps behind a dataset, so when a problem appears, analysts can trace it to the step or source that introduced it. This tracing lets them fix the root cause, decide which derived products are affected, and update downstream results without repeating the entire project.

Question 25

What is the difference between a file based dataset and a database managed dataset?

Accepted Answer

A file based dataset stores spatial data in a self contained file, such as a shapefile or GeoTIFF, which is easy to share but offers limited control over concurrent edits and integrity rules. A database managed dataset stores data in tables under a database system that enforces rules, supports many users, and manages transactions.

Question 26

What is a geodatabase, and what does it add beyond simple files?

Accepted Answer

A geodatabase is a container for spatial and tabular data that can hold feature classes, tables, raster datasets, and relationship classes within one managed structure. Beyond simple files, it supports domains, subtypes, topology rules, and attribute validation, which helps enforce consistency across related layers.

Question 27

What is a raster pyramid or overview, and why is it used?

Accepted Answer

A raster pyramid is a set of lower resolution copies of a large raster stored alongside the original, so software can display it quickly at small scales. Pyramids speed up drawing and panning because the software reads reduced versions instead of processing every cell at every zoom level.

Question 28

What file format considerations matter when choosing a vector format for long term storage?

Accepted Answer

Choose open or widely supported formats that can hold the geometry types, coordinate system, and field types you need. Proprietary or obscure formats can become hard to read, while formats with clear specifications are easier to migrate. Check field name length limits and whether the format stores the coordinate reference system explicitly.

Question 29

Why should GIS datasets be stored with consistent file and field naming conventions?

Accepted Answer

Consistent naming makes datasets easier to find, identify, and join, because a name conveys the subject, scale, date or version, and area without opening the file. Field names that follow a clear pattern also reduce mistakes in queries and scripts, and they avoid truncation problems in formats that limit name length.

Question 30

What is a coordinate precision setting, and why must it be chosen carefully?

Accepted Answer

Coordinate precision is the number of decimal places or resolution at which coordinates are stored, which determines how finely locations can be recorded. Setting it too coarsely can distort geometry and cause features to collapse or misalign, while setting it too finely increases file size without adding real accuracy beyond the source data.

Question 31

What is a spatial index, and how does it speed up queries?

Accepted Answer

A spatial index is a structure, often a tree of bounding boxes, that organizes features by location so software can quickly narrow a search to the features near an area of interest. Without an index, a query must check every feature in the dataset, which becomes slow as data volume grows.

Question 32

How does compression affect stored raster data?

Accepted Answer

Compression reduces the storage space a raster needs by encoding repeated or predictable values more efficiently, which lowers disk use and transfer time. Lossless methods preserve every original value exactly, while lossy methods discard some detail to achieve smaller files, so the choice depends on whether exact values matter for the analysis.

Question 33

What is a data custodian, and what responsibilities does the role usually carry?

Accepted Answer

A data custodian is the person or group responsible for the day to day care of a dataset, including its storage, documentation, quality checks, and access. Custodians typically decide who may edit the data, track updates, and make sure the dataset stays consistent with the organization's standards and policies.

Question 34

Why is version control important for shared GIS datasets?

Accepted Answer

Version control records each change to a dataset so teams know what was edited, when, and by whom, and can restore an earlier state if something goes wrong. Without it, people may work from outdated copies, overwrite each other's edits, or produce analyses that cannot be reproduced later.

Question 35

What elements should a sound backup strategy include for GIS data?

Accepted Answer

A sound backup strategy keeps multiple copies of data, stores at least one copy in a separate physical location, and tests restoration on a regular basis. It should also define how often backups run, what they cover including geodatabases and documentation, and who is responsible for restoring data after a failure.

Question 36

What are the key considerations when sharing a dataset with an external partner?

Accepted Answer

Before sharing, confirm that the data is authorized for release, remove or mask sensitive information such as personal addresses, and check any licensing or usage restrictions. Provide metadata, the coordinate reference system, and a statement of known limitations so the partner can use the data correctly, and agree on how updates will be communicated.

Question 37

How does a data update workflow keep derived products current?

Accepted Answer

A data update workflow defines the steps for editing source data, checking quality, and publishing changes, so that each change is applied in a controlled order. Derived products such as summary maps, reports, and models should be rebuilt or refreshed from the updated source, with records showing which version each product was generated from.

Question 38

What is a data access policy, and why do organizations define one?

Accepted Answer

A data access policy is a documented set of rules stating who may view, edit, or download particular datasets and under what conditions. Organizations define one to protect sensitive information, meet legal and contractual obligations, and make clear to staff which datasets are open, restricted, or confidential.

Question 39

Why should a team agree on naming and editing standards before a project starts?

Accepted Answer

Agreeing on standards early means everyone creates data in the same structure, with the same field names, coordinate systems, and quality rules, which avoids costly cleanup when datasets are merged. Clear rules also reduce disputes about who edits what and make it easier for new team members to contribute without introducing inconsistencies.

Question 40

How should an organization plan for retiring or archiving an old dataset?

Accepted Answer

Retiring a dataset should begin with confirming that no active project depends on it, then noting the reason for retirement in its metadata. The data should be archived in a read only location with its documentation intact, and any links, services, or scheduled processes that point to it should be updated or removed.

GIS Data Management Flashcards

1Spatial Data Fundamentals

2Metadata and Documentation

3Data Quality and Accuracy

4Storage, Formats and Databases

5Organization, Workflows and Sharing

Learning Resources