The definitions used in this glossary are only as a guide for understanding how RivEX works. Underlined words are referenced within this glossary.
Attribute Table - An attribute table contains the non-spatial component of a dataset. For example, a river networks spatial component are the polylines, whilst it's attribute table will contain information like river name, flow rate, water quality etc.
Bifurcation ratio - The ratio between the number of stream segments in one Strahler order and the next. The final segment of a river has no bifurcation ratio as there are no downstream segments to divide with. Literature quote values typically in the range of 2 - 5.
Catchment (Area) - See Drainage Basin
Centre line - This is the polyline that represents the middle of a river channel. RivEX can only process centre-lined river networks. In the image below, the channel on the left clearly shows left and right banks and it's centre-line network is displayed on the right.
The centreline is sometimes referred to as a skeleton or medial axis of the polygon, more information can be found out by visiting the wikipedia link below.
Confluence - The point at which two rivers meet. With regards to a river network it is a To-node shared by two polylines. Note due the nature of river networks, it is possible for more than two rivers to join at a single node.
Cycle (network) - The direction of a polyline(s) is causing a network traverse to go around in a loop. This occurs when one side of a braid\loop is pointing in a sea to source direction. In the image below polylines 246320 & 251608 are flowing in an upstream direction and are thus causing a cycle in the network.
Decimal Degree - The Latitude and Longitude coordinates expressed as decimal fractions.
Dictionary - A data structure used extensively by RivEX which can store "items" that are identified by their "keys". A key can be numeric or a string ID, whilst an item can be anything, even another dictionary. Within RivEX such data structures are used to store node and polyline information for rapid retrieval.
Directed acyclic graph - In graph theory this is a directed graph that has no cycles. In the context of a river network all polylines flow in a source to sea direction such that any traverse of the network will always lead to the mouth of the river and never back upstream.
Drainage Basin - The area drained by a river. Other common interchangeable terms are watershed or catchment area. Click on the Wikipedia icon below for more detailed information on drainage basins.
Drainage Density - A measure of the length of stream channel divided by the area of the catchment. Mathematically expressed as:
Drainage Density = Sum of all stream channels lengths / Area of catchment
Edge - A term used in the study of networks for the link (polyline) between two nodes.
FeatureClass - This is the generic term used by ESRI to mean a spatial dataset.
From-Node - The start node of a polyline. The green circle is the From-Node.
Intersection - The term used when one object is overlapping another. Put into context of a river network this means that a polyline is touching another polyline. If they are touching at their nodes then they are topologically connected. If they are not touching each other at their nodes then network tracing cannot be performed.
Link - The river network can be considered a series of links showing different ratios of link types depending upon the underlying pattern. RivEX identifies 3 types of links: interior, exterior and outlet.
Mouth (river) - The point at which the river meets the sea. With regards to a river network it is the To-Node of the polyline.
Monotonic - The order of the M-values along a Polyline. A polyline can be described as monotonic if the M - values always increase (or decrease) with direction of the polyline. If you have used RivEX to build a measured network then as polylines flow in a source to sea direction the M - values will monotonically decrease as these values are distance from river mouth. The image below shows 3 types of trends, the third being mixed which would be an illogical error in your network.
Multi-Part (polyline) - A shape composed of more than one shape or part. In river networks multi-part polylines are not valid network features.
Network - A collection of nodes linked together. To put in to context of a river network, the centre lines of rivers are captured as a single polyline and linked to each other by their nodes. Polylines that do not link at their nodes are considered not part of the whole river network.If a polyline is intersecting another polyline but not at it's node, then this is an error.
Node - The name given to a polylines' start and end vertex . ESRI terminology now refers to network nodes as junctions. The green circles are the nodes of polyline. See From-Node and To-Node. RivEX can generate and store a unique ID number in the attribute table for each polyline.
Point - A dot which has no size, simply an XY location.
Polyline - A continuous line composed of two or more line segments. Each line segment is composed of two vertices. ESRI terminology now refers to network lines as edges. The order of the vertices dictate the direction of the polyline.
Pseudo node - A node that links only two polylines together. A node at a confluence is not a pseudo node as this represents a junction between 3 polylines. The presence of a pseudo node affects certain types of analysis. In the image below the red points are the pseudo nodes.
Raster - A spatial data format where data is stored in a regular grid of cells (pixels). River networks can often be stored in this format and there are many hydrological tools that process data in this format. RivEX does not process raster river networks.
Recursive (algorithm) - A recursive algorithm calls it self during execution.
Saddle - Are low points on ridges. They are usually flat, wetland regions where streams form and start to flow downstream. It is quite possible to have streams that flow in opposite directions. From a network perspective they are sources "within" a network rather than the ends of a stream.
Shapefile - A standard ESRI file type for storing spatial data.
Sinuosity - A measure of channel length divided by straight line distance.
Shreve (Order) - A stream ordering method which classifies stream segments based upon the number of upstream sources.
Skeleton - see Centreline
Snapping - Snapping is the process of moving one feature exactly to the location of another within a specified search distance. In the context of using RivEX you would snap the end point of a polyline to the end point of another polyline to ensure correct network topology.
Source (river) - The point at which a headwater stream starts. With regards to a river network it is the From-Node of the polyline.
Strahler (Order) - A method of classifying stream segments based upon the number of tributaries. This is probably the most common technique used to order river networks. Click on the Wikipedia icon below for more information on Strahler Order.
Stratified sampling - A population is divided into subsets (strata) and random samples are taken from each stratum. The subsets are typically non-overlapping and every element within the population must be assigned to only one stratum. In terms of river analysis the subset could be catchment boundaries or administrative regions. Each polyline within the network must be assigned to only one catchment polygon. With RivEX you could stratify sampling using catchment areas and ask to sample a % of network by the total stream length per catchment. This would have the effect of generating more points in larger catchments than smaller catchments. Click on the Wikipedia icon below for more detailed information on Stratification.
Stream Order - A method for measuring the relative size of rivers.
To-Node - The end node of a polyline. The blue circle is the To-Node.
Topology - A term used to describe the connectivity of a network.
Valency - The number of edges (polylines) a node is connected to.
Vertex - A single point. Two vertices are required to build a line and many lines build a polyline. The red squares are the vertices of the polyline.
Watershed - See Drainage Basin